Invalid access to memory location using GlobalFree

[Paul McKenzie]

Could some kind guru explain what is a possible cause of this error?

A bug in your program.

Seriously, no one would know what is wrong unless they have your code, run the program, duplicate the error, and start debugging. All we have is your word that your logs and whatever else you're using shows you that things are "OK". So the only conclusion is that your logs are wrong or inadequate in some way. Otherwise, you've discovered a bug in the Windows OS that no one else has encountered (which of course has a probability of occurring at close to 0).

I don't believe I've got a race condition etc

When you are dealing with multithreaded apps, you have to be sure that your code is safe -- not just "believe", but be 100% sure. If it isn't safe code, then you need to be experienced enough to identify and fix any synchronization issues.

Regards,

Paul McKenzie