I was having trouble with my Form2 repeatedly indicating “Resin Sensor Error” during the initiation of a print. Previously there were several successful prints and I reviewed the recommendations on the Troubleshooting page of the FormLabs website; including checking the chip on the resin cartridge, cleaning the chip on the cartridge and on the tray connectors on the machine, reinstalling the tray and twisting to seat, etc. At the suggestion of Tech Support email I reinstalled PreForm software and confirmed the latest firmware installation.
However, the fix I discovered was noticing that the amount of resin in the tray was well OVER the max indicator line printed on the front of the tray. More investigation revealed that the rubber valve on the cartridge was leaking (a slow drip) and between the time of the last successful print and the failed attempt enough resin had leaked out of the cartridge to cause the error. Once realized I acquired a 60cc syringe and removed most of the resin in the tray to the MIN line, dispensed the resin back into the cartridge and restarted the build. There was no Resin Error interruption and have completed 3 successful builds since.
I hope this helps anyone dealing with the frustration of this build error.