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Error message in creating loop

I am trying to build an experiment with audio files and everything worked fine until I tried to build a loop around the main experiment. I was told to let the developers know.
A loop around the practice round worked well, but I can’t create a loop for the main experiment.
Would be very grateful for your advice.
thanks
Jeanine
This is the error message I receive
Traceback (most recent call last):
File “C:\Program Files\PsychoPy\lib\site-packages\psychopy\app\builder\dialogs_init_.py”, line 1455, in onBrowseTrialsFile
returnFieldNames=True)
File “C:\Program Files\PsychoPy\lib\site-packages\psychopy\data\utils.py”, line 420, in importConditions
fieldName = fieldNames[colN]
IndexError: list index out of range