Re: blank page on delete
AdminCP->Styles & Templates->Style Manager->Edit Templates
Are any of your Gallery templates showing as Red? If so, that means you modified them.
Any templates that have been modified in any way, won't be updated to the new version of that template when you upgraded to RC4. Which means they will still have the same old code as RC3, which means they could still have bugs and/or incompatibilities with the new RC4 underlying PHP code. You have to manually revert them to get the new RC4 code.