Hello Shrikant,
Q: If say a user has no data manager activities, I would even expect him not to see the data manager ribbon at all?
A: As far as I know, your perception is not correct, even though he don't have any data manager activities the ribbon is still visible but all the options are grayed out.
one question from my end are you recently upgraded your office version to 2013..?
if yes there is some issues related to office 13, try to upgrade your SP17 to SP22.
If you EPM ribbon doesn't showing any options,Close all the excel opened in your system and then follow the below procedure
please go to Run ==> %temp5%==>Excel8.0==> Delete MSForms.exd
Regards,
Saida Reddy Gogireddy