Hmm. ta.adx() ...
adx() is no build in function for the ta source, at least in version 6 or version 5 what I see in the reference manual.
Where have you found it ? Check the reference and search for "ta.". Lots of build in functions but no adx(). May be there was a self defined method adx() somewhere ? If so you need to get to copy the code.
I am afraid the compiler is right ...