pgodfrin wrote:a brief message in red is displayed
Do you really mean that the message text is short, or are you saying that it's only displayed briefly? If the latter then that possibly implies a cosmetic timing problem between threads.
Also, for host OS your profile only says "MS Windows 7". Is it actually Win7 64 bit?
You may also care to post the .vbox file for the broken VM, as an attachment please.