Outlook 2007 not letting user to send to more than 2 distribution

[russelmiller]

Here is the situation

Outlook 2007
User is attempting to send one email to 4 distributions lists
Hit send "Unexpected error has occurred" (nice and vague)
Try to send to 3 (any combination), same error message
Try to send to 2 it works (any combination)

I have checked all 4 distribution lists for bad email addresses and none,
Also when you expand all 4 lists and send an email it works as well.

Any help is appreciated