I had same problem.

Before install update press Alt-Ctrl-Delete same time, then close WebsiteX5.exe from memory and install update. works for me.

succes

Jan

Iets uitgebreider:

Mayby Website x5 did not close correctly. And it is still in memory, open up your taskmanager, remove all websitex5.exe in process tab. Then try again. Do this during update (directly after the update program has closed X5)

Opening taskmanager depend on you OS. ctrl and shift and escape are the most common keys (all together)
Or
Type in at start -> run -> taskmgr and enter

Hello,

Please check also if the antivirus is blocking the program. Alternatively it can always be downloaded the most updated version from yuor answers.websitex5.com profile in "Downloads".

Many thanks!