If a working stress tipload file does not open correctly in the limit state module you may need to edit the file.
Does the circuit grid look like this after opening the file?
If so, you need to manually edit the file.
1. open the file with notepad
2. at the top of the file find the line with the version number eg version=6.23.631 and change it to version=6.6.0
3. save and close the file
This is a permanent workaround for this issue.