Hi Marius,
To narrow down the root cause of the issue, I'd like to confirm the following information:
1. Regarding "the problem occurs when opening excel files", did the issue only occurs in Excel application? How about opening Word or PowerPoint application?
2. About "I'm now ready to use office", do you mean you have successfully activated Office for Mac and got the following message?
Image may be NSFW.
Clik here to view.
3. After you got the error message "you're now ready to use Office for Mac", can you check whether your machine name is listed in Office 365 portal via browser (Office 365 portal ->click the gear on the top right corner ->Office 365 settings -> Software ->Office)?
After getting the information above, we'll proceed further. Thanks for your time.
Regards,
Alice Wang
