"Keep record files for" not saved in R6 cameras

Hi,
I have 5 R6 cameras connected to a Synology NAS.
I sue iVMS-4200 to manage cameras including configuration.
In iVMS-4200 go in Storage Schedule-->"select a camera"-->" Recoridng Schedule"-->Advance Settings-->Keep record files for XX days-->OK--> Save (right upper corner)
The XX value input there is not saved and it goes back to 0.

Any suggestion?

Regards
Ugo