This can possibly mean that there is a password protected file in the downloads. The best thing to do is to click on the edit customer button

Next click Application Files

 Next you will need to click on each file to download them individually. This will allow you to single out the problem file

Once you have located the problem file, scroll down to the missing documents section and create a missing documents notification for the customer to let them know that the specific file needs to be resubmitted without password protection