End Device Network Layer - saving settings throws error


when I want to make changes to the network layer in the End Device Network Layer settings, I receive this error:

Invalid value of field session.keys.f_nwk_s_int_key.key

This is the case for quite some time now, and other people complain about the very same issue, so I wonder, will this be fixed, or is there another way to change those settings that I am not aware of? Of course all fields carry correct values, and even the attempt to save the unchanged settings triggers the error.

Thanks a lot for any ideas on this, and with best regards