Broken USB driver...?

It seems the USB driver package that Wavecom keeps for at least Q268x-series modules is unable to function when the assigned virtual COM-port-number reaches 3 digits.
What I mean with that is that while an entry is created in the registry, it is not possible to actually open the COM-port.
I have seen this issue myself, and had it reported from my customers.

Connect module via USB
Driver is detected
Virtual serial port COM100 is created
Actually trying to open COM100 from a terminal program results in something like “port does not exist”.

Hacking the registry to assign COM99 to the module instead, and I can connect to it without problems, but this way is not acceptable for end users.
Using the wavecom supplied tool for removing old virtual com port assignments (for wavecom modules) is not acceptable either, as there might not even be any “slots” to remove.

Do other devices work OK with port numbers >99 ?

Yes. (if the program is correctly written, older programs usually get stuck above 8 )
The virtual limit on windows is 255.

i’ve also seen a problem with selima with com-port numbers above 20?
but i really haven’t looked at repeatability of that problem.

I’ve not seen that - well, COM28: was OK, at least…

Other devices I’ve tested work OK with COM >99

The base limit is 255 as Madouc say, though that can be changed in necessary.