Problems when Upgraded to 6.3.5

I have just upgraded from 6.3.4 to 6.3.5 and trying to open any project I am getting an Error message

RapidWeaver could not upgrade your project to the .rw6 format as a file already exists with the name ‘BMI.rw6’.
Please move the existing project file to another location and re-open 'BMI.rwsw"

i have been running RW6 since release and have updated many times but never encountered this before.

Can you please advise…