I am not fully sure what you mean by "not solvable in the latest version". Do you mean that you have upgraded only AnswerTIMES, or the TIMES code as well? Could you also elaborate what you mean by saying that you have "a few times needed to change the type of parameters that is used to make the model solvable"?
If the model should be the same (i.e. you have not made any changes in the model while switching to the new version), I think it would be relatively easy to compare the *.DD* files (and the GEN file), and see if they are different. If they are indeed different, then the problem is probably caused by that, and you can check why they are different under the new version.
If your TIMES version has changed as well, it would also be easy to test with the earlier TIMES version and see if the problem is somehow related to TIMES versions. If you find out that the model still solves with the earlier TIMES version but not with the new, could you then please send me the model input files (*.DD*, *.GEN) for my further investigation, and provide the TIMES version information.
If the model should be the same (i.e. you have not made any changes in the model while switching to the new version), I think it would be relatively easy to compare the *.DD* files (and the GEN file), and see if they are different. If they are indeed different, then the problem is probably caused by that, and you can check why they are different under the new version.
If your TIMES version has changed as well, it would also be easy to test with the earlier TIMES version and see if the problem is somehow related to TIMES versions. If you find out that the model still solves with the earlier TIMES version but not with the new, could you then please send me the model input files (*.DD*, *.GEN) for my further investigation, and provide the TIMES version information.