This is the troublesome part Code (Text): eLeftOutFile = 'data/ElonL'//fileNameSuffix(0:25)//'.dat' OPEN(754,FILE=eLeftOutFile,STATUS='REPLACE',ACCESS='SEQUENTIAL') First off, fileNameSuffix is a CHARACTER(len=40) just to be safe, im just cutting it off, since those are the relevant parameters. Code (Text): WRITE(*,*) fileNameSuffix yields the correct 08V077K1000fsSample1ps, so that string works fine. As you see I'm trying to make a string reading "data/ElonL08V077K1000fsSample1ps.dat" representing the path and filename I want to generate as output. However, the output file ends up JUST being named ElonL. If i remove ElonL and make eLeftOutFile look like 'data/08V077K1000fsSample1ps.dat' then I get forrtl error SEVERE 30. It looks as if the whole string is ignored and the program halts because I try to generate a file with no name in the data/ folder. First time poster, so please ask any questions if I've been unclear.