Volvo - intermittent code CFFF - SRS-CFF Controle Module - Internal Fault.

The code is intermittent and MaxiSys cannot erase, with messages "engine running or fault not repaired"... if it it intermittent, why can I not delete it? I understand if it is a permanent fault but not when intermittent (live data works, so module seems to be working right now?).

I followed procedure; start car, rev 1500+ rpm, turn off, start and idle +20seconds, then push ok (for erase).

also tried when turning key off after running idle.