MSG Compactlogix to Compactlogix

I had the same Issue, I double checked the lists to make sure all data types were the same.

I found that when I imported the user-defined data structure I changed the name (that is when it did not work)

When I imported the user-defined data structure the second time I left the name alone, and it worked.

Take a look under the Controller properties, then Capacity tab. See if the ethernet nodes used to close to maximum? Then also see if your memory capacity is below the total by a meg? This way you can be sure if your not running out of memory or ethernet nodes.