I had the same error using Oscam with channels that cannot be decoded temporarily (on German Sky channels after the change of encrpytion last November). From the log you can see, that Oscam is re-sending the requests in short intervals after the server send a "not found" reply (so different to "server takes to long" and requests runs into a timeout, what can be specified in the Oscam settings as well). In the case the timeout settings specified in oscam.conf (fallback timeout and client timeout) are not working - as it is no timeout, the server respond directly with "not found".
I got it under control with configuring ratelimit settings for each reader in oscam.server (only necessary for "readers" that have trouble on server side). For my dual login account I use:
ratelimitecm = 2
ratelimittime = 7500
On single login account (not for receivers with 2 active tuners) ratelimitecm = 1 will be correct.
Usually I only decode one channel a time, I am not recording so much or using picture-in-picture and thats fine for me, but with 2 active decoding channels from the same PayTV package I recognize that it takes some more time to switch channels. With a normal account (no dual login) and ratelimitecm = 1 you should recognize slower performance on switching channels on the same PayTV package every time (might take 2-3-4 seconds in addition to start decoding) but it solves the problem
!! and as I said: on a dual login account while receiving only 1 channel its no problem at all, or I am really switching channels to fast.
As long as the cs-server is having no trouble and all codewords are correct the problem will not occur because Oscam is not re-sending the request immediately to the server as Oscam do after receiving the "not found" replay (or any other return from the server that makes Oscam to respond directly with an action).