Well I've just tested on UAE and I'm a bit puzzled...
In DP 3, I can't reload any image : no error message at all.
In DP 4, I can't reload any image : Message box "System message - Can't Load <filename>"
Maybe it's the versions I'm testing (4.0, copyright 85-91 Electronics Arts) or I should configure UAE for a different hardware (currently: OCS)
In any case, I tested with a file saved on DP2E, it won't load either...