Strange problem with Upload Centre affecting SharePoint and Excel VBA

We were stunned that this had affect a macro that we have written in Excel that simply wrote some files to a SharePoint site.

For some reason, it refused to write the files all of a sudden. It would refuse to write any file to a particular folder.

eg \\mydomain.com\sharepoint\shared documents\mmm

It would error everytime the macro ran.

However, just a change in folder, it would start to work again.

eg \\mydomain.com\sharepoint\shared documents\mmx

We could not work out why until, by chance opening the Upload Center

Guess what, it had previously error-ed on a file that was trying to upload to the same folder in SharePoint.

 \\mydomain.com\sharepoint\shared documents\mmm

It would then start blocking all files to the same location until you delete all of the cached files by pressing the "Delete Cached Files" button in the "Settings".

Really mad that it would block all subsequent writes to the area just because of one previous error.  Anyway, we learned the hard way and now will not forget to check this when we encounter this again.