Error 22 (Invalid argument) - any ideas what causes this?

Version 6.12.65-20
Sangoma A500 BRI ISDN Card 8 x Active channels

The log is full of these:

NOTICE[2571] sig_pri.c: pri_check_event returned error 22 (Invalid argument)

The system seems fine, No ‘reported’ errors from users

Is this something that can be ignored?

Regards

Dale