slinky

I'm having a problem with an AOI I have created from standard ladder logic. The Ladder code works fine outside of the AOI.   The code is manipulating strings and also pulling them from a 1 dimensional array. It generates a message header (STRING) , then pulls the relevant message (STRING) from an array and concatenates them. This is done 50 times, using a JMP LBL loop.   Are there some limitations of loops/timing within an AOI that may be affecting the code execution? I believe I read about this a long time ago, but can't find any reference.   PLC is an L72S   I have one last thing to check before I am lost for options.  

Please could anyone share PLC, HMI and anything else(documentation etc.) for examples of car plant controls systems? Please