As a Exchange administrator, I get to dodge this particular Outlook RPC-dialog pop-up issues for users. Sure enough, everyone must have seen the following dialog box at some point of time.
Let see the following excerpt from this MSKB 892764
You receive this message as part of the standard inter-operation of Outlook and Exchange. Even on the fastest network that has the best hardware and architecture, some remote procedure calls will take more than five seconds to obtain a response. This is a simple fact, and the appropriate expectations should be set with users. If the message appears only occasionally, no extensive troubleshooting is required. Trying to troubleshoot when the message appears only occasionally is not likely to be productive.
So, it’s not completely avoidable. It’s a way of life for Exchange server and it’s Outlook clients.
At one point of time, an administrative assistant complained she consistently gets Outlook RPC dialog when she is accessing her boss’s calendar to manage. It turn out to be the calendar she is accessing has 11000 appointment items AND that is a real issue according to Microsoft. Check this MSKB 905803 below.
Other usual causes are Remote Public folders, Huge Mailbox, Outdated Network card driver, Slow access to Global Catalog and Corrupted OST file.
Check out the following URLs also:
Check my latest blog about troubleshooting this issue: http://anandpv.spaces.live.com/blog/cns!AFCCA5892B178862!657.entry