While working with the VMware vCenter Converter Standalone Client (in my case version 5.0) I kept getting the following error while trying to convert machines:
A general system error occurred: SQL_CANTOPEN: unable to open database file
After some research I find this error message has been around for awhile and also happens with previous versions of the Converter. Some say network errors can cause it.
In my case it was the CrashPlan backup client that was causing it. Forcing CrashPlan to sleep during my conversions corrected my issues. I also read that for some disabling antivirus software corrected it for them.
So basically anything that could be locking files on the computer your running the VMware Converter software on is where you should look and not the machine being converted. It was driving me crazy and I thought it was the target VSphere Server that was the issue.