MySolution.WSP has an unsupported extension, and cannot be added to the solution store

A member of my team busy with SharePoint deployment industrialization came to me with this strange error message resulting from a “usual” STSADM –o addsolution command.

I quickly skip the detailed enumeration of the usual suspects (corrupt CAB, system A-V, path with spaces…) to jump straight to the real cause: STSADM (or the SharePoint API) handles the file name’s extension with case sensitiveness and therefore did not support having the filename parameter’s value containing .WSP while with the actual file name is is .wsp! We adapted the script to rigorously use the same file name as it is in the file system and it finally worked as usual… Wow, SharePoint has some hidden *NIX behavior sometimes ;)

And cut!