When I attempt to sync Mambo with the 190+ users I have in SMF, I only get up to the E's when I get this error:

Syncing username Esteve-O Failed! Please enter a valid Username:. No spaces, more than 2 characters and contain 0-9,a-z,A-Z

I don't know why it would fail, but is there any other way around this error?
I am using Mambo 4.5.2.3, SMF 1.0.5, and Mambo-SMF integration 1.3.1.3.