I don't fully understand your post. Please excuse my ignorance. I have inserted the code you supplied and I don't get that error any longer. Does that mean that the logfile was never closed at the end of setup like I thought I was?
Next, how do I access the files to write to them if I can't do that from loop. I thought I had seen examples that did exactly that but I may be mistaken. What do you mean by
A far bigger problem is that you cannot get any performance if you open and close files in loop. You need a rxFile and a txFile that are opened in setup().
Are you saying that I need to open the files in setup and just leave them open? Would having separate functions open, write and close the files outside of loop work better?
Pseudo code:
if there is something on the UART line for tx, goto the Tx function open file, record whats in the serial buffer for that UART and write to the SD card file for TX, then close file and return to loop. Then do the same for Rx? Thanks for the guidance. Sorry for being such a noob.