AGi32 v17.3 (or greater) job files containing a Page Builder Report with a locked Master Page are NOT backward compatible! The program will crash and display the error 'RTE 35601 – Element not found’ when attempting to access Page Builder in earlier versions.
Unlock or remove the Master Page before sharing a AGi32 v17.3 (or greater) file with someone using an earlier version. Ideally, only share files with someone using the current version!
Currently, there is no possible 'fix' for this compatibility issue. Please use the Workaround!