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The full text of the error message is:
*** Error 336 in ... This version of GAMS does not allow the declaration of variables and equations. It is intended to run precompiled models only. If you need a fully licensed GAMS system contact your distributor or GAMS Development Corporation
This error indicates that you are using a GAMS system, which has a runtime license installed. As the message says, this license intended to run precompiled models only. If you want to make some experiments, you should use a GAMS installation that is either a fully licensed version or (if the model is small) that has no license at all.
With no license at all, GAMS will work but will enforce size restrictions on the models it will solve. If you have installed GAMS on your machine just for learning purposes you must have copied your companies runtime license file and can just delete it from your installation. The name of the license file is gamslice.txt.
If your machine needs to use the runtime license but you also want to use it for learning GAMS you can override the reading of the license file. If you are using the GAMS IDE, just put