scenario.solve() error in 3.11.1 version

[cheolhung]

What happened?

After upgrading MESSAGEix to v3.11.1, I attempted to run the Westeros baseline scenario, but encountered an error during the execution of scenario.solve(). I have attempted several troubleshooting steps based on guidance from ChatGPT, but the issue persists. I would appreciate your assistance in identifying the cause and resolving this error.

---

Exception Traceback (most recent call last)
File MsgScenario.java:1328, in at.ac.iiasa.ixmp.objects.MsgScenario.toGDX()

Exception: Java Exception

The above exception was the direct cause of the following exception:

java.lang.UnsatisfiedLinkError Traceback (most recent call last)
Cell In[28], line 1
----> 1 scenario.solve()

File ~\anaconda3\envs\message_env\Lib\site-packages\message_ix\core.py:753, in Scenario.solve(self, model, solve_options, **kwargs)
734 def solve(self, model="MESSAGE", solve_options={}, **kwargs):
735 """Solve MESSAGE or MESSAGE-MACRO for the Scenario.
736
737 By default, :meth:ixmp.Scenario.solve is called with 'MESSAGE' as the
(...) 751 :class:.MESSAGE_MACRO class and :class:.GAMSModel.
752 """
--> 753 super().solve(model=model, solve_options=solve_options, **kwargs)

File ~\anaconda3\envs\message_env\Lib\site-packages\ixmp\core\scenario.py:894, in Scenario.solve(self, model, callback, cb_kwargs, **model_options)
892 # Iterate until convergence
893 while True:
--> 894 model_obj.run(self)
896 # Store an iteration number to help the callback
897 if not hasattr(self, "iteration"):

File ~\anaconda3\envs\message_env\Lib\site-packages\message_ix\models.py:506, in MESSAGE.run(self, scenario)
503 self.var_list = self.var_list or []
504 self.var_list.extend(variable.gams_name for variable in REQUIRED_VARIABLES)
--> 506 super().run(scenario)

File ~\anaconda3\envs\message_env\Lib\site-packages\message_ix\models.py:242, in GAMSModel.run(self, scenario)
239 lines2 = ("{} = {}".format(*kv) for kv in self.cplex_opts.items())
240 optfile2.write_text("\n".join(lines2))
--> 242 result = super().run(scenario)
244 # In previous versions, the cplex.opt file(s) were removed at this point
245 # in the workflow. This has been removed due to issues when running
246 # scenarios asynchronously.
248 return result

File ~\anaconda3\envs\message_env\Lib\site-packages\ixmp\model\gams.py:423, in GAMSModel.run(self, scenario)
419 s_arg["container_data"] = self.container_data
421 try:
422 # Write model data to file
--> 423 scenario.platform._backend.write_file(
424 self.in_file, ItemType.SET | ItemType.PAR, **s_arg
425 )
426 except NotImplementedError: # pragma: no cover
427 # No coverage because there currently is no such Backend that doesn't
428 # support GDX
429
430 # Remove the temporary directory, which should be empty
431 self.remove_temp_dir()

File ~\anaconda3\envs\message_env\Lib\site-packages\ixmp\backend\jdbc.py:616, in JDBCBackend.write_file(self, path, item_type, **kwargs)
613 raise ValueError("write to GDX requires a Scenario object")
615 # include_var_equ=False -> do not include variables/equations in GDX
--> 616 self.jindex[ts].toGDX(str(path.parent), path.name, False)
617 elif path.suffix == ".csv" and item_type is ItemType.TS:
618 models = set(filters.pop("model"))

java.lang.UnsatisfiedLinkError: java.lang.UnsatisfiedLinkError: no utiljni64 in java.library.path: C:\Users\Cheolhung\anaconda3\envs\message_env\Lib\site-packages\tutorial\westeros\apifiles\Java\api;C:\Users\Cheolhung\anaconda3\envs\message_env\Lib\site-packages\ixmp\backend\jdbc\AMD64

Code Sample

What did you expect to happen?

.

Versions

(message_env) C:\Users\Cheolhung>message-ix show-versions

ixmp: 3.11.1
message_ix: 0.0.0
message_ix_models: (not installed)
message_data: (not installed)

click: 8.3.1
dask: 2026.1.1
genno: 1.29.1
graphviz: (not installed)
ixmp4: (not installed)
jpype: 1.6.0
Java VM path: C:\Users\Cheolhung\anaconda3\envs\message_env\Library\lib\jvm\bin\server\jvm.dll
openpyxl: 3.1.5
pandas: 3.0.0
pint: 0.25.2
xarray: 2025.12.0
yaml: 6.0.3

iam_units: 2025.10.13
jupyter: 5.9.1
matplotlib: 3.10.8
plotnine: 0.15.2
pyam: 1.6.0

GAMS: 24.8.3
system dir: C:\Users\Cheolhung

python: 3.13.11 | packaged by conda-forge | (main, Jan 26 2026, 23:43:44) [MSC v.1944 64 bit (AMD64)]
python-bits: 64
OS: Windows
OS-release: 11
machine: AMD64
processor: Intel64 Family 6 Model 142 Stepping 11, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None
LOCALE: ('Korean_Korea', '949')

### Additional Context

_No response_

[khaeru]

Hi @cheolhung —this issue is incomplete, so it is missing information that we would need in order to identify the cause of and solution to your issue.

In particular, under “Versions” you would have seen this text.

If you edit the issue description to include this info, that will help.

[cheolhung]

Hi @khaeru,
I’ve added the full “Versions” details above—could you please take a look?

For context, I’ve been developing and running MESSAGEix-KOR on version 3.3 without any issues so far. However, since 3.3 is now quite outdated, I’m planning to upgrade to a more recent release. Not only the tutorial scenario, but the base scenario of MESSAGEix-KOR, which worked fine in version 3.3, is not working in version 3.11.1

I would appreciate your guidance on the best upgrade path and how to address this issue.

[khaeru]

Thanks @cheolhung for the additional info!

I see the following:

ixmp: 3.11.1
message_ix: 0.0.0

Based on your comment, I take it you are using message_ix 3.11 with ixmp 3.11. The fact this shows "0.0.0" is a known issue: iiasa/ixmp#583.

GAMS: 24.8.3

I’ve been developing and running MESSAGEix-KOR on version 3.3 without any issues so far. However, since 3.3 is now quite outdated, I’m planning to upgrade to a more recent release.

I think this is the root cause of your issue. See the release notes for ixmp 3.10 (from 2025-02). In short:

• ixmp (and message_ix) now use GAMS library files that are installed with GAMS itself. Previously, ixmp included duplicates of these files.
• However, this only works with more recent GAMS versions. In those 2025 releases, we also updated these installation instructions to indicate which GAMS versions should be used. Please read these carefully.
• Because your GAMS version is much older, the ixmp code cannot find these files. This is the proximate cause of the error java.lang.UnsatisfiedLinkError: no utiljni64 in java.library.path.

Thus my suggestion would be to update your GAMS version. Per the install instructions I linked above, please try the latest version if possible.

Once you've done that, please leave another comment with (a) updated show-versions output and (b) any new error message you see.

[cheolhung]

Thanks @khaeru for your response.
I will get back to you once I update the GAMS version.