The error message is due to an invalid expression ("Syntax error: '-' can't go here - are you missing something before it?").
Construct 2 had some bugs where it incorrectly allowed invalid expressions. Construct 3 is more robust and verifies expressions more correctly. However it means if your C2 project relies on a C2 bug that allows an invalid expression, it won't import in to C3. You'll need to open it in C2, find an invalid expression using '-', fix it, save and then it should import to C3.