Thanks Art -
Error 50 seems to be a card issue for DR40. I took the opportunity to do some housekeeping ( tough for me ) and edited my SD card through a card reader and computer, and saved everything I wanted to keep in one folder on the computer. This was the original card and has never been fully erased or re-formatted. When I put the card back in the DR40 it said "no music" or "no files", damn if I remember which but the opening recording screen was there. Then I could use the DR40 menu to get to "SYSTEM" and thence to FORMAT and executed the FULL FORMAT. That takes about 20 minutes or so and now I've got my baby back. It would be nice if Tascam offered a list of what the SYSTEM ERROR codes mean for various units and what we can do to go at least one step further. I've written to them but the online SUPPORT queue is likely miles long. If I hear from them this year I'll let you know. Going out on a limb here, since this unit is from around 2014 it probably wouldn't be such a bad idea to upgrade the firmware. Thanks for taking the time to give us all some options. I'll be saving your valuable info.