Need Help; Having trouble uploading PDFs in our meeting rooms

We have a problem of PDF files that do not upload properly.

When uploading a file from computer, we often get an error message:-

"There was an error converting your file .

There may be security restrictions on this document "

Here are some of the symtoms of the problem :-

1 . In some cases, after leaving it a while, and trying again later, the problem has gone.

2.  In other cases; one Host cannot upload a PDF file, but when another Host tries to upload the same file in the same meeting, it works.

3.  Or in other cases, the Host cannot upload a PDF file in one meeting room, but can upload the file in different meeting room.

     This means that all other users in the first meeting room have to switch to the other meeting room in order to view the Host's PDF file.

So it does not seem to be a "security restrictions" or file configuration issue,since the same file works perfectly at some times and not at others

and with some users and not others

It seems to be escalating with more cases coming in our meeting rooms everyday, and I do not know how to give Support for this issue.

Has anyone seen or heard of this issue elsewhere ?

Is there any fix we can find for this ?