Please provide more information:

-What form were you trying to e-mail? (ie. AR Statement)
-What version of the module? (ie. 8.1 (070601))
-What is the error message?
-At which stage in the process does it occur?
-What happens exactly?
-Does it happen everytime?
-Did e-mailing work before?
-If so, has anything changed on your computer?
-Are you e-mailing from the same computer where you defined the e-mail settings?