Disable desktop switching with the scroll wheel in Lubuntu?

Starting with Lubuntu 14.04 or earlier, the config file format and solution became slightly different from @SWrobel's answer. Then in Ubuntu 17.10 (or earlier), things changed again.

The following instructions apply to the current situation (Ubuntu 17.10 and later).

1. Remove the following lines from ~/.config/openbox/lubuntu-rc.xml to disable any scroll wheel desktop switching in a window, with and without modifier keys. (Keep the outer <context …> … </context> element though.)

   <context name="Frame">
     […]
     <mousebind button="A-Up" action="Click">
       <action name="GoToDesktop">
         <to>previous</to>
       </action>
     </mousebind>
     <mousebind button="A-Down" action="Click">
       <action name="GoToDesktop">
         <to>next</to>
       </action>
     </mousebind>
     <mousebind button="C-A-Up" action="Click">
       <action name="GoToDesktop">
         <to>previous</to>
       </action>
     </mousebind>
     <mousebind button="C-A-Down" action="Click">
       <action name="GoToDesktop">
         <to>next</to>
       </action>
     </mousebind>
     <mousebind button="A-S-Up" action="Click">
       <action name="SendToDesktop">
         <to>previous</to>
       </action>
     </mousebind>
     <mousebind button="A-S-Down" action="Click">
       <action name="SendToDesktop">
         <to>next</to>
       </action>
     </mousebind>
   </context>
   

2. Also remove the following lines to disable any scroll wheel desktop switching on the desktop background:

   <context name="Desktop">
     <mousebind button="A-Up" action="Click">
       <action name="GoToDesktop">
         <to>previous</to>
       </action>
     </mousebind>
     <mousebind button="A-Down" action="Click">
       <action name="GoToDesktop">
         <to>next</to>
       </action>
     </mousebind>
     <mousebind button="C-A-Up" action="Click">
       <action name="GoToDesktop">
         <to>previous</to>
       </action>
     </mousebind>
     <mousebind button="C-A-Down" action="Click">
       <action name="GoToDesktop">
         <to>next</to>
       </action>
     </mousebind>
     <mousebind button="Left" action="Press">
       <action name="Focus"/>
       <action name="Raise"/>
     </mousebind>
     <mousebind button="Right" action="Press">
       <action name="Focus"/>
       <action name="Raise"/>
     </mousebind>
   </context>
   

3. Also remove the following lines to disable any scroll wheel desktop switching while moving a window around:

   <context name="MoveResize">
     <mousebind button="Up" action="Click">
       <action name="GoToDesktop">
         <to>previous</to>
       </action>
     </mousebind>
     <mousebind button="Down" action="Click">
       <action name="GoToDesktop">
         <to>next</to>
       </action>
     </mousebind>
     <mousebind button="A-Up" action="Click">
       <action name="GoToDesktop">
         <to>previous</to>
       </action>
     </mousebind>
     <mousebind button="A-Down" action="Click">
       <action name="GoToDesktop">
         <to>next</to>
       </action>
     </mousebind>
   </context>
   

4. Execute this to let the settings take effect immediately (source):

   openbox --reconfigure
   

cd ~/.config/openbox
cp lubuntu-rc.xml lubuntu-rc.xml.bak

(this makes a backup file so that when you think you've messed it up you could revert it back.)

leafpad lubuntu-rc.xml

and delete the lines which says;

<mousebind button="UP" action="click">
 <action name="DesktopPrevious" />
<mousebind button="Down" action="click">
 <action name="DesktopNext" />

Log out and Log in back again to see the changes!

if you've messed it up and want to revert it back;

cp lubuntu-rc.xml.bak lubuntu-rc.xml

Answer quoted from Lubuntu docs