[Blackhat]

Im using 3.8.1 and get this error when sending mass pm

ERROR!
The following errors occurred when the system tried to send PM to the above users. No PM sent.:

Array
(
[0] => The following users were not found:

1. little_billy_&_big_fred


)

I tried ignore it and clicked next and got this

ERROR!
The following errors occurred when the system tried to send PM to the above users. No PM sent.:

Array
(
[0] => The following users were not found:

1. O'
2. Fal'
3. Shia Kor'
4. Vesa Tau


)

and this goes over and over again on every page.

When I choose not to send PM to users who have disabed PM it works