[EpiData-list] Lost all my code as a result of a system error

Yesterday I was working on a questionnaire (over 300 variables) and at an advanced stage, got this message "Access violation at address 0048AC7 in module Epidata.exe. Read of address 00000000". I lost the whole work after it will not allow me to save. I started anew but this time I backed up the chk file at different stages of the developmeent of code (has a lot of skip patterns and replace of values in all places which have been skipped). The problem has appeared occurred agian and naturally have lost the code I was building from this afternoon. Has this happened to anyone before and if so how did you resolve it?

Thanks in advance

Martin