You will have to go through the documentation of the libraries, because there is nowhere specified about the errors for GSMComm. I have tried finding all the possible solutions, but with no success. There were other users who encountered the same issue, but not viable solutions were posted or found. If you have the readme or help files for the library, use the contact options to get in touch with the developer of those libraries. This way you can get information about error codes and possible bug fixes.