"Failed to Load" workflow in Sharepoint Designer

i ran across this error today when attempting to open existing workflows, and found several posts which indicate the 12.x.x.xxx folder under \Documents and Settings\\Application Data\Microsoft\SharePoint Designer\ProxyAssemblyCache need to be deleted (after closing Designer).

this didn't work in my case.  it did allow me to create new workflows, but i wasn't able to open my existing ones.

and then i remembered the other day, i was troubleshooting a different sharepoint issue and in doing so, i replaced web.config with an earlier copy.  it didn't fix my other issue, but i also didn't restore the web.config to the later version.

so, i put the latest copy of web.config back in place, renaming the older, "safe" copy of the file.  i then deleted the 12.x.x.xxx folder, and launched SPD.

and there was much joy & singing across the land.