Todays L4D2 update has stripped the symbols from the Linux server binary, unless Valve reverse this decision (the server binaries for all their games other than CS:GO are unstripped in order to support modding), it will likely be a significant amount of time before SourceMod is fully supported on L4D2 again.
Valve have released a new update with the symbols restored and most things are now working again. This is just a regular major update now, and will need various gamedata updates as issues are found. SM itself seems to all be fine.
Any threads made about issues with the update will be closed and redirected or merged here.
Threaded Mode