.pdf files wont upload to Adobe Send & Track

I have two Adobe Send accounts.  I use the Send & Track function to get notifications when the .pdf files I send are viewed and downloaded.  I have been using this service for several years without any problems however last week I began getting the error message "One or more files could not be uploaded.  Please try again".  I retried the same file several times, when that didn't work I tried different .pdf's that I had sent earlier and which had previously uploaded and sent however I got the same error message.  I signed out and back in, restarted my computer etc. but still I get the same error message every time.  Next I logged into my other Adobe Send account and tried sending the same files through Send & Track.  This time, and in my other account, the files uploaded and sent without problem.  I then logged out of my second account and back in to the former and attempted to send the exact same pdf's on the same computer and browser however I got the exact same a for mentioned error message every time.  The majority of the files I send originated in Excel which I then save as a .pdf to be emailed.  I originally thought that something may be going wrong when .xlsx files are converted to .pdf but the fact that one of my accounts works and the other does not seems to remove that possibility.  Finally I contacted Adobe Support to see if it was a payment issue and its not.

Thank you so much for any help or advice you can offer.