Struggled to get a Silverlight Application to load in the browser. Checked and double checked that the .xap mime type was succesfully registered. It was working correctly on our other machines.
The .xap file was in a folder called ClientBin. Tried connecting directly to the xap in the browser by navigating to it directly, and it was found, something that wouldn't have happened had the mime type not been correctly registered.
Turns out the cause was a 'Debug' folder that was also in the folder where the .xap file was located. Although this folder was empty, for some reason silverlight was checking/looking here anyway even though the source setting in the object tag was set correctly. Removing this empty folder solved the problem.