Batch Processor Says "File Missing" When Project Is On External Hard Drive

From an external hard drive, I sitched a bunch of panos with Hugin. The original files are on an external as are the .pto files. I had to unplug the external hard drive with a lot of projects left to process in the batch processor. When I turned on the computer and plugged in the extrnal again and started the batch processor, all the remaining projects say "File Missing" and will not reset, start, restart or otherwise process.

I ran the stitcher again for a few of these in the stitcher and when I save them, it asks if I want to replace the existing files. I say yes and the batch processor works as it should.

The question is, why does the batch processor say "File Missing" when a subsequent run of the stitcher creates and saves the exact same file in the exact same loction that the batch processor doesn't seem to be able to find from the previous time the stitcher was run and is there any way to get the batch processor to recognize those files it thinks are missing but had no problem finding before the computer was turned off and the hard drive removed and then turned back on with the hard drive connected to the same USB port. No folder names were changed either.

Thanks!
--Adam