Diagnosis
That's usually the bucket float switch itself getting stuck or the little board it plugs into (the bucket switch PCB) getting corroded. Humidity in a crawl space is brutal on electronics.
How to Fix It
Unplug the unit. Pull the bucket out and look at the black plastic float switch assembly on the left side inside the bucket slot. Manually flick the little white paddle up and down a bunch of times—sometimes it just sticks. While you're there, unplug the white connector that goes from the float switch into the side of the unit. Check both the connector and the socket for any green corrosion or moisture. Clean it with some electrical contact cleaner or even a dry toothbrush if it's just dusty. Plug it back in firmly and test.
If That Didn't Work
The control board might be misreading the signal. There's a known issue where the board needs a reset. Unplug the dehumidifier for a full 5 minutes. Plug it back in and immediately press and hold the "ON/OFF" button on the control panel for 10 seconds. This sometimes clears a phantom sensor error.
Heads Up
If you keep having this issue, the float switch or the PCB is probably failing and needs replacement. Santa Fe sells a kit, but you can find the part number (usually something like 620105) by searching for "Santa Fe Classic bucket switch assembly."