Doesn't open when space in path

[Guest]

A file C:\Documents and Settings\mypath\image.jpg
When you double-click on this file in explorer an error message is displayed:
"Error opening the file <C:\Documents>"

[ckit]

Using RegEdit check this entry:
HKEY_CLASSES_ROOT\XnView.jpg\shell\open\command
"C:\Program Files\XnView\xnview.exe" "%1"

It's important that there is "%1" and not %1

[helmut]

A file C:\Documents and Settings\mypath\image.jpg
When you double-click on this file in explorer an error message is displayed:
"Error opening the file <C:\Documents>"

Please have a look at FAQ "How to associate image files with XnView". I guess you are novice user and recommend to use the stable release, which currently is XnView 1.80.3.