You could have a couple of problems going on. If your stealing bills and they are going into the Stacker, but not on top of the Stacker pusher plate then the validator is trying to reject the bill and if it can’t the validator will steal the bill, this is normal. If it’s happening a lot then you could have a problem with the validator, harnessing etc., these problems can be a bitch to find and fix. If you’re getting bills on top of the Stacker pusher plate then the stacker isn’t cycling to push the bill down. Check the spring on the side of the Stacker, they sometimes break. If it’s broken it’ll be loose and you’ll be able to push the stacker plate up about an inch or so. The Stacker on the XE validator is controlled by the Controller if you got a problem with your harnessing you could have stacker issues. A 1.6 error code could be that the bills are balling up not going into the Stacker or the rear gate on the validator isn’t dropping fast enough or hanging up. Cleaning the validator will not help when you have a rear gate issue, the only option is to send the validator in for repair. When was the last time it was serviced? What version software is the validator? You want to be using v3.55 software.