What kind of operating system are you using?
If on UNIX/Linux check if the key files are assigned to user pixadm and group sapsys and can be read by user pixadm, i.e. check ‘ls -l‘ command in directory /usr/sap/PIx/DVEBMGS0x/sec for the output like
-rw-r------ 1 pixadm sapsys 345 20. Jul 21:34 Kennametal-PRIVATE.asc
Check ACLs if on Windows Server.