Unable to open .msg attachment via QC

Hope someone can help :)

Each time a user tries to open an attachment in QC, which is a .msg format - outlook throws up an error saying "The command line argument is not valid. Verify the switch you are using"

Googled and googled and googled, nothing helps - the file type association is correct as outlook attempts to open... but doens't get any further.

The .msg file integrity is good, can open fine if you save it to the desktop etc, but i want to be able to have users open it directly via QC.

Anyone else seen or had this before?

Thanks,
Jack