I haven't looked at the SOC, but there are a number of things that can cause a SOC to cause C-Failures.
If the SOC uses A_FindTarget, it may be inertly flawed, and will never be netplay compatible.
If the SOC uses A_SmokeTrailer, this is a flawed function, and you'll wanna switch to A_SpawnObjectRelative.
If the SOC uses A_MoveRelative, A_BunnyHop, or something similar, it may be propelling the player too fast for the autoadjust to keep up. Go to Global Game options and disable automatic adjustment of animation tics.
That's all I know of right off the bat, may edit with more.