See issue #104 which is similar. If you put the same 4 lines of code in a predicate definition instead:

int counter;
counter = 0;
counter = 1;
eq(counter, 4);

Then when I run the planner, I see this exception:

terminate called after throwing an instance of 'EUROPA::PSLanguageExceptionList'

Again, there is nothing wrong with the model, and the planner should be able to handle this case.

hmm, I'll have to review the grammar, "=" should not be allowed there, if you're imposing a constraint, use == instead.

My mistake. "=" is not allowed there. I was editing a simple example in a text editor and didn't realize the issue. When I type it into Tatiana's editor, I get a nice red marker on that line. :)