I've seen it happen when the original VMBX has problems. Sometimes there have been attachments embedded within the VMBX with invalid filenames (the file name is either too long or has too many periods). The VMBX embedded attachment header breaks up the filename poorly and stuffs it all up.
If it's an isolated thing then it's the VMBX.
Personally I've been helping customers convert all their VMBXs to MSG or EML. Easiest for the long term as VMBX is very unique to TRIM.