Squish: AUT: Cant copy files to remote device

Following situation: We are working with an AUT, which copies local files to a virtual X: for using the files remote on a device. On all other systems like windows 7 it works fine but not on windows 10. I’ll get following errormessage:

Couldn’t copy file ....\global\testdata\fileXYZ to X:/user/testCustomUser : [Errno22] invalid mode (‘wb’) or filename ‘X:/user/testCustomUser/’

Does anyone know anything about an Errno22? The problem is, the method which creates folders e.g. testCustomUser, if it does not yet exists, works fine on windows 7 but not on windows 10. I have to create the folders manually on X: when I start the run of the testcase.

best regards