Hi mpaterson,
Did you install the beta version of Visual Studio before? If you installed any pre-release versions, you may encounter this issue. To fix this issue, please uninstall them by following the steps in the link below.
Uninstalling Previous Versions of Visual Studio 2005
http://msdn2.microsoft.com/en-us/vstudio/Aa718704.aspx
For your reference, you may try to download the troubleshooting tool to scan the Visual Studio. This tool was discussed in this article:
How to fix Visual Studio Class Designer Package load failure in VS 2005 after beta 2 uninstall
http://blogs.msdn.com/astebner/archive/2005/08/27/457248.aspx
VS 2005 troubleshooting tool
http://astebner.sts.winisp.net/Tools/ttool.zip
In addition, there is a similar thread posted in our forum. I hope it is helpful.
Package Load Failure
http://forums.asp.net/p/936819/1111646.aspx