Hi and thanks for reporting.
However, this is indeed a limit as imposed by your Exchange administrators :(
, a post reports it maybe doesn't handle frequent network disconnects very well and multiple sessions per user build up on Exchange (not sure which version).
For Outlook 2010,
a blog describes
increasing the open item limit on Exchange 2010, along with
a more detailed MS Technet article
If you're lucky, trying OGCS again another day after you have logged off and Exchange has dropped your sessions, you might have better luck as your colleague did. If not, what version of Outlook are you running? Is it exactly the same release or patchset as
your colleague? If not, maybe you can request an upgrade.
Finally, if your IT run an Exchange cluster, it might be different servers have got different settings, and you're connected to one with more restricted configuration.
Anyway unfortunately, there's nothing I can do to help with the application - so I hope you have friendly Exchange administrators who can help. Good luck!