Help with Applescript

 I need help with extension writing in Applescript for Alfred.
This following script works, it sets the mouse sensitivity to 5.

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set trackingValue to 5

--Open and activate System Preferences
tell application "System Preferences" to activate

--Attempt to change settings using System Events
tell application "System Events"
        tell process "System Preferences"
                try
                        --Open the "Keyboard & Mouse" pane
                        click menu item "Mouse" of menu "View" of menu bar 1
                        delay 2
                        set value of slider "Tracking Speed" of window "Mouse" to trackingValue
                        --end tell
                on error theError
                        --An error occured
                        display dialog ("Sorry, an error occured while altering Keyboard and Mouse settings:" & return & theError) buttons "OK" default button "OK"

                end try

        end tell

end tell

if application "System Preferences" is running then
        tell application "System Preferences" to quit
end if
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I want to make an extension for Alfred which does the same thing but the user can specify the value.

What's wrong with this? i don't know much about Applescript and thought you might be able to help me. Thanks in advance anyway.

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on alfred_script(q)

    set trackingValue to q

    --Open and activate System Preferences
    tell application "System Preferences" to activate

    --Attempt to change settings using System Events
    tell application "System Events"
        tell process "System Preferences"
            try
                --Open the "Keyboard & Mouse" pane
                click menu item "Mouse" of menu "View" of menu bar 1
                delay 2
                set value of slider "Tracking Speed" of window "Mouse" to trackingValue
                --end tell
            on error theError
                --An error occured
                display dialog ("Sorry, an error occured while altering Keyboard and Mouse settings:" & return & theError) buttons "OK" default button "OK"

            end try

        end tell

    end tell

    if application "System Preferences" is running then
        tell application "System Preferences" to quit
    end if
end alfred_script

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