Can't export map module: Sharing Violation

Hey folks, I'm having a hell of a time exporting a map module I made for the Masks of Nyarlathotep campaign. I keep getting this error:

"Unable to save file <map file name> to package file <module file name>: Sharing violation on path <module file name>"

Does anybody know how to fix this?? There's no modules imported, it's an empty campaign other than the images / maps that I've added LoS onto. That's it.

Thanks in advance.