In order to perform a Typo3 update from 4.3.2 to 4.5 LTS, I updated to 4.4 and to 4.5 subsequently.

Before doing the first update step, I updated the extensions. The update process broke up with the error "Error: The extension MD5 sum could not be fetched from extensions.md5.Possible reasons: Network problems, allow_url_fopen is off, cURL is not enabled in the Install Tool". I checked allow_url_fopen in php.ini and whether PHP cURL was enabled. Both was correctly set. I found that the repository mirror link delivered a strange XML file that looked binary, although it's supposed to be XML. The existing repository URL was http://repositories.typo3.org/mirrors.xml.gz. After replacing it with http://typo3.org/mirrors.xml.gz everything worked fine.

Another issue occured when entering the install tool of Typo3 version 4.4: No CSS or images were loaded within the script. The apache log said "[alert] [client xyz] /xyz/typo3/contrib/.htaccess: ExpiresActive not allowed here, referer: http://xyz/typo3/install/index.php?TYPO3_INSTALL[type]=config" I changed the AllowOverride directive in the Apache vhost to All and it worked as expected.