Another error we encountered after the kernel upgrade 7.20->7.21 was repeated SSF_KRN_SIGN_BY_AS message in system log SM21.
My advice is to search some notes first. There is plenty of information.
The full line of the error was:
SSF_KRN_SIGN_BY_AS: Function Returned 5
For us the solution was very simple.
Run transaction STRUST.
Open “System PSE”
There we had an entry host_SID_InstNr in red. – However on the right side, under “Own Certificate”, under “Owner” we had only “CN=C11”
which is quite inaccurate.
Right click on System PSE and choose Replace. Accept defaults.
Now host_SID_InstNr is green.
The warning in SM21 repeats no more!