"Symbolic" mode fixed it for me
I realize this is an old thread, but I just ran into an identical problem and this article came up when I was searching for solutions. So I'm posting the solution I found for the future greater good.
I was having exactly the same symptoms. My application was using Kepware to poll data from an AB CompactLogix L35E.
The solution was to edit the properties of the PLC node in the Kepware tree, change the Protocol Mode (in the Logix Options tab) to "Symbolic", and then make sure it STAYS Symbolic after you click the Apply button. Be careful: the mode may revert to the previous mode and you might not notice it. Someone once told me they change the Data Collection mode (in the General tab) to "Disable" before trying to change the Protocol Mode. Even that did not work for me. I had to delete the old PLC node in the Kepware tree and create a whole new one with the Symbolic mode from the start.