Issue testing recurring payments

I'm using the test API and am having problems putting through recurring payments. Non recurring payments are working fine. This is the response I'm getting:

 

{"response":{"vs":"true","rc":"null","message":"Could not process transaction","authcode":"null","transactionkey":"ot-jvKfFtaSsdsfesfSESF2","refnum":"null","statuscode":"","statusmessage":"","txnnumber":"null","recursuccess":"null","note":"","env":"test"},"vs":"true","rc":"null","dk":"ot-jvKfFtaSsdsfesfSESF2"}

 

Why am I getting "vs" as true, but "rc" as null?

Any help would be greatly apprecated.