I've had this happen before and had to start the report all over to get around it. Just happened again today on another report.
I was trying some different expressions in the print_if field of a region. I would try previewing the report to see if it worked or got an error, then edit the expression and try again. At some point, the expression disappeared from the print_if field, but every time I try previewing I get an error that's coming from that expression. I can't get past this as I can't find the errant expression anywhere to delete it.
How do I fix this so I don't have to start the report all over again?