Hazel File is busy. Skipping for now.

I am trying to move a number of image files (100s) with a rule which is very simple:
if Kind = Image:
do the following: Move top x Drive.
in doing so I get an error Hazel File 2013_08_10-125.cr2 is busy. Skipping for now.
the debugging brings back this additional information.
2023-03-28 21:56:32.194 hazelworker[3099] DEBUG: Found 'brok' file.
2023-03-28 21:56:32.194 hazelworker[3099] File 2013_08_10-125.cr2 is busy. Skipping for now.
2023-03-28 21:56:32.194 hazelworker[3099] DEBUG: Tapping busy retry sequence.
Can anyone suggest what maybe going wrong?
Paul
if Kind = Image:
do the following: Move top x Drive.
in doing so I get an error Hazel File 2013_08_10-125.cr2 is busy. Skipping for now.
the debugging brings back this additional information.
2023-03-28 21:56:32.194 hazelworker[3099] DEBUG: Found 'brok' file.
2023-03-28 21:56:32.194 hazelworker[3099] File 2013_08_10-125.cr2 is busy. Skipping for now.
2023-03-28 21:56:32.194 hazelworker[3099] DEBUG: Tapping busy retry sequence.
Can anyone suggest what maybe going wrong?
Paul