I am getting the same error "you must use absolute path" in the attached program (related to 2nd frame of the structure). Could anybody please help me with this issue?
If you want us to look at your code, it would be nice to have a smaller reproducing case, especially one that does not contain third party driver VIs. Could you try creating a copy of this VI and stripping it down to the smallest reproducing case that you can?
Otherwise, a nice tool to make sure that the filepath does exist and that this error shouldn't occur would be to use the "Check if File or Folder Exists" VI. Here's a link that talks a little about how the VI works.
Did you solve your problem by removing the illegal characters? Then please mark the solution.
(While we are at it, you should also simplify your code. For example your inner FOR loops are way too convoluted and could be done with much less code. No need for shift registers and all that.)