I don't know what that particular error means, but if it's happening for all debit transactions I would guess that there are 3 possibilities:
1) Your PINPad has not been injected with an encryption Key - it actually has to be sent to the bank to be injected at their facility.
2) Your Merchant account has not been set up to accept Debit (on the Banks End)
3) Your Account information has not been correctly or completely entered into Store Operations Administrator.
What version of RMS are you using? You can find this by opening any of the Store Operations programs and going to Help/About. StoreOperations SP2 added some additional fields for Debit Cards, so if you are not upto at least SP2 that may be your problem.