Hi Makari,
Were you able to resolve this issue? You might try clearing your browser cache as a first step. Note that we've just released v3.1 of the Viewer and API, so you can try upgrading to these.
http://resources.arcgis.com/en/communities/silverlight-viewer/index.html
http://resources.arcgis.com/en/communities/silverlight-api/
Hope that helps,
Katy