Sometimes even the Pro Tools Expert team have problems with their Mac and Windows machines. 

On Monday evening (why is it always late in the day) I was configuring a Mac system to go out on a live recording job. I had hooked up a Universal Audio Apollo 8P to my 13" 2013 MacBook Pro via Thunderbolt and launched Pro Tools to be greeted by this error:

"Pro Tools is trying to install a new helper tool. Enter your password to allow this"

Once I entered my password I was again greeted with the same message and was stuck in a loop. With a bit of searching, I found the answer on the DUC and would like to share it with you now so if you too get this error you will know how to fit it. 

Navigate to Mac HD (Your system drive) > Library > PrivilegedHelperTools and delete all the files in here with Avid in the title. 

When you next launch Pro Tools it will again ask for your Password but it will accept it and continue to start. 

Many thanks to Selle Sellink on the DUC for this one.  The general consensus is that this could be something to do with connecting to Universal Audio Apollo hardware but, to be honest, I'm just glad I was able to fix it.