I think the main problem is that one AV may see another AV's virus signature file as a threat, and attack it as being full of viruses. One AV may also detect activity to read (or clean/quarantine) an infected file as suspicious, and block it. So, it is certainly possible to have one AV interfering with the activities of another. If you disable WD to run the other AV, it's possible that parts of WD may be damaged by the other AV. Can you back up all the WD files first, so they can be restored if necessary?