error attempting to read from the source install.... error during install

I am trying to install build 797 of R# 4. I have an earlier build installed.

I am getting this error during installation:

"Error attempting to read from the source install database: c:\windows\installer\a471c8.msi". The name of the file is different every time I try an install as I assume it's a random temporary name. The file exists in that folder.

Abdu