Uninstall of v9.4 client breaks another application

[gtonkin]

A client recently opted for the upgrade to v10.2.2 FP4 instead of trying to go the self-cert route for SSL.
3 client PCs running Perspectives were uninstalled and loaded with v10.2.2 FP4 32-bit.
The client now has an issue on all 3 machines where an application that was being used no longer works. The application appears to be a "normal" windows application and does not use any IIS or similar web components (may predate the web!)
The application is proprietary with no logging or support - it starts, says it has stopped, closes.

We thought it may be down to removal of ASP.Net v2, C++ Redistributable, MSCharts or other prerequisites, but these all seem to still be in place.
I cannot find any uninstall logs to interrogate either.

Has anyone had this before? Any ideas, suggestions are welcome!

[gtonkin]

OK, so re-installing v9.4 client somehow magically fixes this 3rd party application!?!?
Will have to peruse the 13Mb install log to try and see if anything jumps out.

Any ideas on what may have broke and why still welcome.