For some reason I have some really old files with blank last modified properties. Romcenter crashes trying to fix the name on them. The error says it is because of the timestamp.
I tried fixing the file through powershell, but it won't update (changing creationtime and accesstime works fine). I ended up using the following command in dos to fix the file:
type BombJack.d64 > BombJackNew.d64
I deleted the old file and Romcenter recognized the new file as a valid rom and fixed the name.
At the very least, you might add checking the modified timestamp in a try/catch to keep the software from crashing to desktop.