Private Message error

[Gert Vw]

Hello everyone,

Since today all usergroups can't send no new PM's anymore to each other. If you try it says : "You have entered an invalid recipient". Even when the username is correct.
Reply to messages/conversations they had already is the only way now to communicate to each other.

Someone who can help me with this error?

[sunrisecc]

http://community.invisionpower.com/4bugtrack/405-unable-to-send-private-messages-r5858/