I have encountered this very same issue and have found that if you EXPORT the script, it unlocks the IMPORT script option on the menu. However, if you intuitively click on IMPORT to bring in a new script (replace), it just brings in the same script that was exported. However, if you click on PROPERTIES, you can import a new script. Hmmmm... Does that help? 2 yrs later! hahahahaaa : ))