Never encountered this specific error before, so I'll just be able to offer some mindmapping:
- Is your savetype set to Flash 512k (2.6) or Auto (2.6a)?
- Do you have enough free space on the drive you run No$ from?
- Does your drive have any write-protection that might be enabled (in case of an external HD)?
- Is No$ decompressed?
- Do you have other games that can save?