Yes I know, this is a slightly dated software, and by slightly I mean a lot. However, when someone has issues we do what we can to help.
The error message in the trace log says 363: Type System.Workflow.ComponentModel.Serialization.NullExtension is not marked as authorized in the application configuration file
The application says "can't publish workflow" (might have been "can't compile workflow"). This happened earlier and I found a blog about a lot of authorized types in web.config which solved those. All the old issues could be from a .Net upgrade which I found on a Sharepoint blog.
Regarding this issue, no hits on your favourite search engine to help me. My first thought was to install UR 21 which wasn't installed on the server, however the server was installed with Swedish as base language and Microsoft have removed the UR21 files in Swedish, only English is still availabel, dead end!
Since the last one was solved by adding an authorized type I started looking in the web.config and I actually found a line which looked slightly similar to the error
Version=220.127.116.11, Culture=neutral, PublicKeyToken=31bf3856ad364e35"
TypeName="TypeExtension" Authorized="True" />
Sooo, I simply added another line where I changed the TypeName to "NullExtension" and did an IISReset and the old server was publishing workflows again.
Sometimes I just feel that you're not supposed to be doing these things, don't know if it's supported or not but it worked...
Developer at CRM-Konsulterna