I have been trying to make a flight plan from L373 Leiston (an Ian Elliot airfield downloaded from SimOuthouse) to EGSS Stansted, using the @ symbol, and I get errors all the time.
Can anyone post one here that starts around 12 noon please?
Sometimes it better to start simple, ie a 24hr return with no @, and make sure that compiles, then add the other features one at a time, making sure it compiles each time. If it doesn't you know where the problem lies.
The @ symbol is known to cause problems with flight plans, I'm sure there is another thread on here about it somewhere.
Get ttools202.zip from AVSIM. You might never use the tool, what with AIFP being the compiler of choice these days, but the TTools readme.htm has one of the best explanations of what each individual bit of a flightplan means with examples.
From this topic and the last time you asked for help with a flightplan, it looks like you don't really master the flightplan format. The Traffic Tools readme is a must read to get started.