We just released a new version of ReviewBoard+PowerPack, you can download here. I am trying to reproduce the issue with this version but everything works fine for me.
I also tried to reproduce the issue in the concrete situation of having already installed another application using Apache and MySQL. This case also worked for me, the only difference is that I need to install it on port 81 and 3307 instead of 80 and 3306, but everything works fine.
Can you try with the new version? If the problem persists, can you copy here the output of two commands?
ps aux | grep httpd
ps aux | grep mysql
Carlos R. Hernández