I cannot tell you the correct Swedish, as I translate SW->EN, but my guess is that this refers to the POST technique used with HTTP to return a command plus data from a browser to a webserver (see first reference below for explanation - for example it is likely that when I send in this explanation, proz is using POST to handle it).
So I suspect that POST does not need to be translated. It is just an error message to say that the server is expecting HTTP POST data, but none has arrived, or else that it has arrived but as GET or HEAD data (see 2nd reference for definitions)