Private Messages Error For Some Users

[DavoteK]

Version: 4.1.15

Since updating, getting an error message when sending a PM. They can compose, but upon sending, it fails and gives an EX4086.

System Logs gives me this error;

ErrorException: Argument 1 passed to IPS\core\Messenger

Any ideas?

[SaltyBart]

 

[DavoteK]

Many Thanks.