This problem seems to be caused by the query parser. The error message can be reproduced by the following procedure: (open the attached project "test.xml". Notice, that there is an intentional syntax error (space between "E" and "<>") in the query): 1. Load project test.xml; 2. Go to query tab and press "Model check". Then the error message "E: Unknown identifier" appears (if one presses "Model check" again (not necessary for reproducing the error) without changing anything, one is prompted with "syntax error, unexpected T_GT" message); 3. Change the state space representation to "Options"->"State space representation"->"Under approximation"; 4. Press "Model check". Then error "CAUGHT EXCEPTION: Invalid variable type" is prompted. It does not matter if the syntax of the query has been corrected or not. If "Model check" is pressed again, "Fatal error: Broken pipe The server connection has been killed." error message is prompted.
Created attachment 16 [details] model for reproducing the error
This was actually caused by the fix for bug 58. The implicit declaration of the unknown variable 'E' would modify the model, thus causing a crash when the model is instantiated. A fix has been checked into CVS.