Decrypting files on XP

[Meech]

Windows certainly does not auto-encrypt anything. This is most certainly an operator error type thing.

[OrcaDK]

You're SOL. Your file was encryptet based on a asymmetric algorithm meaning that the key to decrypt your file was stored in your old windows user account. If you have deleted that account without saving the proper account certificates, you'll have a hard time decrypting the file.