outlook 2011 error code -50

Hi all,

 

  I am new to this forums, I am running into a strange issue with outlook 2011. I will give the details of what we use etc. We use exchange 2007 server. Client is using outlook 2011 with the most recent updates (14.3.6). Whenever she gets a meeting invite from an external organization, and when she accepts it with response / without response, it throws her an error -50 Mail could not be sent and the meeting response moves to outbox. For now we have asked her to accept any meetings outside our organization to accept via her phone. 

I am trying to reproduce the same error but its only her outlook which is giving issues. Please advise.

Thanks,

Regards,

Pre