Microsoft released an update to Silverlight 4 (4.0.50826.0) which fix incompatibilities with building and deploying Silverlight projects built on a developer machine that also has LightSwitch Beta 1 installed (SL version 4.0.50630.0). This'll also mean that you can now test deploying a LightSwitch Beta 1 app to another machine. Existing customers will be automatically updated to latest Silverlight version via WU. If you already have installed this latest version of Silverlight on a development machine and then install LightSwitch Beta 1, the latest version of Silverlight will be used so no incompatibilities should exist.
Here're relevant highlights KB2164913: SDK feature to enable Add New Row capabilities in DataGrid control; Improving startup performance of Silverlight apps; Adding mouse wheel support for out-of-browser apps on Mac platform; Various media-related fixes around DRM content; Fixed memory leak when MouseCapture is used; Fixed memory leak for DataTemplate usage.
Download: Silverlight 4