We use Reference Manager Network V 11.01. We have had several occasions when a user has created a new database, closed it, reopened and been asked to upgrade it from V8/9 to V11 even though the user has not got V8/9 installed on their computer.
I have yet to figure this out – we also get this message frequently for people who have never used RM 8/9.
It happens slightly more when we have network connection problems (we have the network version of RM), which might be the cause of an index file corruption, but we also often have the convert message when there are no network problems at all.
This only worked for one person, but you could try uninstalling & reinstalling RefMan?