error on custom distribution list

we are in the process of migrating to exchange from an outsourced email solution. one of my users has several distribution lists in their contacts. when they try and send a message to one of their distribution lists they get an error of “unexpected error has occured” i have tried researching this and have tried several things to figure this out to no avail. there is nothing in the logs. i am going to try installing SP 2 for office 2003 to see if it fixes anything.