Malcolm,
I have never used XceedEncryption (am very new to VFP) but if you are looking to encrypt a string why not do it yourself.
Do something along the lines of;
Function ENCRYPT
PARAM _PassWord
_Encrypted = ""
For _Pass = 1 to LEN((ALLT(_PassWord))
_Encrypted = _Encrypted + CHR(ASC(SUBS(ALLT(_PassWord), _Pass, 1)) + INT(LEN(ALLT(_Password)) * (_Pass + 12)))
Next
Return _Encrypted
(Like Harry Potter's schooling, I can't do anything without a spell checker)