Q:

Windows 7 64 Bit/Save mode: Rename msi.dll not possible

Due to problems with the windows installer 5 I must rename msi.dll for reinstallation. That's not possible in save mode/as administrator (access denied). Of course the service is stopped. Any hints?
Edit: My problem is that I can't install msi files anymore. Everytime after some dialogs I get an error message that the corresponding msi file can't be read. I have tried any infos I found in the www universe and lost a lot of time already. E. g. I replaced the registry settings, used sfc /scannow without success.
In Windows 7 there is no dllcache, so I really don't know what is preventing renaming.

A:

My problem is that I can't install msi files anymore. Everytime after some dialogs 
  I get an error message that the corresponding msi file can't be read

This sounds a little bit strange. If you see MSI dialogs and the install fails when you kick it off there must be something else wrong. I assume you have, but have you verified that the problem exists with multiple MSI files? Try with a fresh MSI file, preferably one that you downloaded fresh from the Internet. Try to run from the local disk and from a network disk.
Have you enabled logging for the install? Try to do so with flush to log enabled (the ! character enables continuous flushing to log so that an msiexec.exe crash doesn't leave an empty log file):
msiexec.exe /i C:\Path\Your.msi /L*vx! C:\Your.log

See msifaq.com for more details (logging faq entry). Search for "value 3" in the log file to find errors as explained by Rob Mensching (Wix & Orca author).
Also try to disable any anti virus software and / or desktop security that may be interferring with the file extraction from the MSI's cab file. Is there plenty of disk space? Are there any errors found during a disk scan?

