Hi Ivor,
You have to recompile tslib with changes as described here
http://www.ptrackapp.com/apclassys-notes/embedded-linux-multitouch/
to solve this issue. Key is replacing any occurence of ABS_X / Y with ABS_MT_POSITION_X / Y in input_raw.c.
Then copy and replace the new lib and executables in target system.
This should solve your issue.
Ram