Invalid Parameter - C-File

I am writing on behalf of a colleague:
He (Dorico version 5, Win 11) can’t open two of his recent Dorico projects.
He would get a warning „Ungültiger Parameter“ which is “Invalid Parameter”.
By checking the file type in Explorer the file has turned into a “C-File”.
Anybody with a good idea - or has this happened before?

It sounds like perhaps a problem with the filename of the Dorico project or perhaps the complete path to the project. Could you zip up and attach the troublesome projects?

yes, thank you.
Here are the two files: (768.3 KB) (764.3 KB)

that was easy. I unzipped his files: because he named the files “Telemann_Vl-B.c.”
(B.c. short for Basso continuo)
Windows stripped the last dot and turned it into a .c file :joy:
I added .dorico after this and the file opened no problem: “Telemann_Vl-B.c.dorico”
Telemann_Vl_B.c.dorico (990.0 KB)
Telemann_Viola_B.c.dorico (967.4 KB)