@Herrmann_wst
I know this is an older post but I will respond in case it helps someone with the same error. I agree it appears to be related to how the widget handles the date format pulled from the APC UPS EEPROM.
I ran into the same error after replacing a battery and updating the "battery change date" in the EEPROM. After this change the widget threw the same error as you have posted.
In troubleshooting I referenced the APCUPSD user manual and noticed it shows two different date formats: BATTDATE [ mm/dd/yy | dd/mm/yy ] ... Last battery replacement date. Maximum of 8 characters.
When I saw this I remembered that when I changed the date using APCTEST it had prompted for the "DD/MM/YY" format.
This made me also think it might be related to the date format so I updated the battery date again using "MM/DD/YY" just to test, and this resolved the widget issue in my case.
Summary:
stop APCUPSD service
ssh/ open shell
run apctest
select option #5 to program EEPROM
select option #2 to change battery date
update as MM/DD/YY to make widget happy :)
save, quit and exit shell
restart service and enable daemon /NIS
enable widget and check dashboard
Hope this helps.