It just saying you have not configured a boot system comman in the saved config and
the boot system used would be default.
1. Change the config register setting to 0x2102
2. Configure boot system flash
or boot system flash; if you have more than one image in flash.
do "wr mem" again and see if the problem still occurs.
Its not a performance affecting error, its more informational than warning
and if its still present after above, then its just a cosmetic bug.