I use a third party compression tool from XCEED.  I have copied the two
files, “Xceed.Compression.Formats.dll” and “Xceed.Compression.dll” into the
App_Code folder on the web site.  I have these lines in my web.config file:

<assemblies>
 <add assembly="Xceed.Compression, Version=3.3.7113.3050, Culture=neutral,
PublicKeyToken=BA83FF368B7563C6" />
 <add assembly="Xceed.Compression.Formats, Version=3.3.7113.3050,
Culture=neutral, PublicKeyToken=BA83FF368B7563C6"/>
</assemblies>

These dlls are NOT added to the GAC on the server, but shouldn't  I be able
to do an xcopy deployment like I can with a windows application?

I get a runtime error every time I try to start the web site as long as
these references are there.

copying it all to my local machine (where the XCEED components are installed
into the GAC) and it works fine.

Thanks!