Would hazard a guess it may be tied to different versions of a DLL getting loaded. WoW may have nested it's own version if a Visual Studio file in it's install folders and it is causing a problem. Could try enabling/updating both your .Net 3.5 and 4.x installations (launch the add/remove programs snap-in from control panel(or appwiz.cpl from search/run box) and verify both versions are enabled with the link to turn Windows features on/off. V3.5 may be listed under a legacy category).