This error often occurs as the result of "link-hacking". In other words, grabbing a previous action's link and appending the new action's key to the end of it. If the actions are of different styles (ie. action3 versus action4) then this error will occur.
It can also occur when launching the action from an outdated Action Listing.
The best way to ensure that you're loading the appropriate URL for your action is to access the action in Salsa, and use the 'Show Publishing Tools' section to launch the action: