Calendar error will give an specific error message on the screen (same text).
It's possible that there's traces cut by corrosion on the 68000 bus. If you get the monitor test pattern when you turn it on without a cartridge, the cut trace is towards the cartridge connector.
Now, there's a few things to test:
1- all dip-switches down, to force it to test the WORK RAM.
2- Place a MULTIBIOS (any version will do) on the BIOS slot to attempt to troubleshoot the issue
3- Track down any traces of corrosion, with SPECIAL attention to the backup memory area, because the battery is specially caustic and sometimes leak material, causing board damage (hence Laurence's suggestion).