Another workaround that doesn't require you to copy any files:
Go to System/Preferences/Startup Applications, and edit the UPS Monitor entry, and change the Command field to this:
/bin/sh -c 'cd /usr/share/icons/gapcmon && /usr/bin/gapcmon'
This just changes to the icons directory before executing the apc monitor.
Another workaround that doesn't require you to copy any files:
Go to System/ Preferences/ Startup Applications, and edit the UPS Monitor entry, and change the Command field to this:
/bin/sh -c 'cd /usr/share/ icons/gapcmon && /usr/bin/gapcmon'
This just changes to the icons directory before executing the apc monitor.