yeah, I can imagine…
Id say (whilst you wait for a response from Squarp)
a) format sdcard, and try some tests saves on it. or alternatively (safer?) try a different sdcard.
(obviously backup project first on to your computer !)
b) if you have the error again (Id hope not on new card!), try save as, if save fails.
generally using ‘save as’ to store backups is a pretty good idea
c) check the sdcard, there should be a backup directory, you may find a copy of the project there, that is loadable , assuming you had previously saved it successfully.
also make sure you are on latest firmware version. (partly as this will the first thing you are asked, if you have support issues )
btw: if you still have your ‘corrupted project’ , zip it up and place it on dropbox/google drive , and we can take a look … to see if its a corrupt project file or if there is nothing there… if there is little there, then id suspect it was an sdcard fault.
btw2: if the corrupt project has some midi files you could check those in a daw, see if you have any track data that you could ‘salvage’.