I installed TortoiseSVN-1.14.0.28885-x64-svn-1.14.0.msi over an existing installation (from TortoiseSVN-1.13.1.28686-x64-svn-1.13.0.msi).
I did not close any of the programs the installer reported as having to close, but instead rebooted after the installation.
When I logged on, I got an error, that tortoissvn could not find the file libapr_tsvn.dll .
I looked into the installation directory and it was right: This file was missing.