Hello
The SUM tool is scans the upgrade directory where you have put all the files for the EHP6 upgrade along with the stack file you have generated.
The phase you are right now is doing this and it failed with the above error.
Possible causes are files which are required for the upgrade are either missing or corrupted.
Go to the log directory /tmp/SUM_AIX/SUM/abap/log and check ALL the most recent logs.
I can see that you are using the /tmp file system for the upgrade which I don't personally recommend for any upgrade activity.
If SUM_AIX is a directory created under the /tmp file system you need to make sure that the /tmp file system is sufficiently large enough to complete the upgrade activity. Check the size of the /tmp file system.
If you need assistance you need to provide the recent logs generated by the upgrade tool from the log location.
Regards
RB