Target Tracker Run time error

[Little-Miss]

Whenever staff go to update a group in Target Tracker they get the error "Runtime error 381 Could not set the list property. Invalid property array index". For those who've never used TT, its built on Excel, using loads of clever macros and things! lol

 

Now this is installed on machines throughout school via GPO and the issue had been reported so far on 3 or 4 machines. I have tested it on my machine and am getting the same issue. I tried a repair and a quick uninstall and reinstall which doesnt seem to have worked.

 

any other suggestions? What can make a piece of software stop working like this? An update?