For some reason, Metamod: Source has ceased to load into L4D1 lately for me.
An 'Unable to load (file directory of MM:S)' message pops up when loading L4D1 into -insecure mode.
No message occurs for a dedicated server.
I got the latest MM:S version, downgraded it to an older version I used before that worked, I even installed a brand new L4D1 dedicated server, but it's still refusing to load.
The only thing I can think of is having gotten a (modified) copy of the L4D1 demo placed in C:\Program Files (x86)\Left 4 Dead Demo. The demo somehow synced with my L4D1 settings in the Steam Cloud when I loaded it... could I have triggered an anti-piracy feature of MM:S?