Thanks for the report, you are not the only one with that problem. Unfortunately, I have not yet been able to reproduce the problem myself, and I have so far not been able to pinpoint the cause of the problem. Maybe you can help me shed some light on the circumstances?
-) First, which versions of Joomla and VirtueMart do you have installed exactly? VM 2.0.20a or some older version?
IS it a new installation, or did you upgrade Virtuemart from earlier 2.x versions?
-) Second, which languages have you configured in VirtueMart (do you have a multi-lingual shop?) -- see Configuration -> Shop -> Languages Settings.
-) And what are the joomla frontend and the joomla backend languages?
-) Third, do you have multi-vendor mode enabled in VirtueMart (Configuration->Shop->Advanced Settings)?
-) I suspect that it is some kind of database error. One thing that might solve the problem is to let VirtueMart try to fix the database structure:
Can you go to "Tools -> Tools & Migration" and clicki on "Install or if necessary update tables". This will not delete your data, it will just make sure that all database tables have the correct format. For this to work, you first need to enable "Enable database Update tools" in "Configuration->Shop->Advanced Settings" (if it's not enabled, VM will tell you with a message).
Does this solve your problem?
It would be great if you could help me track down the cause of the problem, which has eluded me so far (since I can't seem to find the correct settings to reproduce it, I really rely on user feedback to find out when the problem appears).
Thanks a lot,
Reinhold
PS: Two users have reported that the problem disappeared after they upgraded their VirtueMart installation from 2.0.10 and 2.0.14 to 2.0.18, so maybe it is really a database problem...