This could be because BetterZIP does not
report supported file-types in it's PLIST.
You need to add ".zip" file association for that application, if it's not yet there.
In Finder, control-click BetterZIP.app, select "Show Package Contents".
In Contents folder, select info.plist.
Open info.plist using Property List Editor.app, available on the OS-X distribution disks in the developer section,
or use regular text editor, NOTE: edit it as a regular text file, NOT Rich Text format.
Next to "Root", option-click the disclosure triangle to see all values.
Scan the values, edit the values by clicking on them.
Find section
<key>CFBundleDocumentTypes</key>
You need to create something like the following section -
<dict>
<key>CFBundleTypeExtensions</key>
<array>
<string>zip</string>
</array>
<key>CFBundleTypeName</key>
<string>ZIP Archive</string>
<key>CFBundleTypeRole</key>
<string>Editor</string>
</dict>
Reboot your Mac and everything should work.
Send here Info.plist from BetterZIP, so i can take a
look if this is indeed the source of your problem.
Regards,
Max