Error while executing testsuite with 2 identical testcases

[Guydzin]

1. Open testsuite which was created earlier
2. Add testcase (identical testcase is already in testsuite)
3. Run testsuite with Chrome browser
4. Get an error without any details:
   
   

UPD:
This case reproduses only when you edit and run existing testsuites.
Didn’t reproduse in newly created testsuite.