-- Is a proper .Net version installed on the problematic box?
Yes its a .NET 3.5 SP1/WPF application. As I'm on Windows 7, .NET 3.5 SP1 is included with the OS.
-- Was this version of .Net installed prior to TestComplete?
Yes, included with the OS.
-- Was TestComplete reinstalled/repaired if .Net was installed after
TestComplete?
Not applicable but I will attempt a repair on TC anyway, perhaps another part of my development environment is messing with it.
-- Are all relevant Extensions installed in TestComplete?
It ssems to be so. I'll attempt a repair however.
-- And finally :) - Does tested application contain debug information as
per AQA's recommendations?
In this particular case no. Though I've been testing Release builds of this app for 2.5 years, only to now have this occuring again... I can switch to full debug builds that include both the debug assemblies and pdb's if I have to.