When I log into my Teamspeak 3 client, it tells me an update is available, and do I want to install it. A Yes click starts the process, which stops and chokes at 59%. The error report log displays the following:

Previous update session for v. 14345 found
Starting update process
Download / check product ini
Compiling download and replace list
No downloads needed
Starting file updates
add/replace QtCore4.dll._z_
add/replace QtGui4.dll._z_
add/replace QtNetwork4.dll._z_
add/replace accessible/qtaccessiblewidgets4.dll._z_
add/replace changelog.txt._z_
add/replace error_report.exe._z_
add/replace imageformats/qgif4.dll._z_
Could not delete 'C:/Program Files/TeamSpeak 3 Client/imageformats/_old_qgif4.dll'
rolling back file updates
Update cancelled

How do I fix this? Several other people in my gaming clan have had similar problems.