Can't read Cab-file

[Sweens]

When I try to install a program from cd-rom, Easy CD creator or Ms-Office, I get the message that the installer can't access the Cab-file.
When I copy the contents of the cd-rom to the HD, the installation runs smoothly.

I think I've messed up a setting or service. Does anyone know what can be the cause of this problem ?

Thanks and greetings