I haven't seen that error occur before as a result of our product being installed. How intriguing.
If the error is to be believed it's telling you Outlook was installed per User, not per Machine. Now, how that control has anything to do with our code is mystifying.
If the error is not to be believed, as in it's totally erroneous - that Outlook failed somehow and the failure was handled by this particular routine... well, then your guess is as good as mine.
Something you could/should try is leaving VSE installed and instead:
a) disable the Email Scan feature from the VirusScan Console (or ePO policy if ePO managed)
b) open Outlook with its safe mode option, and within the Advanced settings uncheck the EmailScan add-in
Determine if either of these options allow for Outlook to open for this User.