>I've written a couple of routines for my customer to encrypt several fields in a table, so that the data can't be copied & taken off site
>
>I've used the "_cryptapi" class, (customers preference)
>
>Using the class if I encrypt a string, decrypting it gives me my original string, but when I put the encrypted string into the original field that the string is from in the table, when I read it back later and decrypt it I sometimes get the right results, sometimes I don't.

You should make the field varbinary or blob to avoid padding problem. Also you have to specify encryption provider because default is different between Windows versions.