The problem you're encountering is a known bug in Photoshop CS5.1's Dutch Help. Luckily, however, there is a solution! 8-)
1. Exit both the Adobe Community Help application (if it is open)
and Photoshop CS5.1.
2. Go to http://help.adobe.com/HelpCfg/nl_NL/P...
3. Save the file that appears in your browser (File > Save Page As) to
the appropriate directory for your operating system:
* Windows XP/Vista/Win7 32 bit
C:/Program Files/Common Files/Adobe/HelpCf...