While using some variables and string functions i have found bug where if parenthesis are anywhere in the string it brakes the function and just shows the call.
so if you put in
{STRING(Substring|TestString1|0|4)}
you get
TEST
but if you put in
{STRING(Substring|T()estString1|0|4)}
it outputs
{STRING(Substring|T()estString1|0|4)}
Which when trying to read a file to get date/header infomation to append to a file name then causing the full function call to be appended to the file name causing illegal characters in path and failing the job.