You may need to clear your PLC. I would try to connect to it via the Communications Link, NOT your Project .dmd file. PLC->Clear PLC. Close the Online project, then open your Disk project and after connecting try to write your project to the PLC.

If you cannot connect to the PLC, you will have to do it using dipswitches and the magic handshake. This clears everything, so you will have to reconfigure your IP Addressing, so write all that down. See Designer help topic DMD0266 On-Board DIP Switches. Look for the Clear All section towards the bottom of the topic.

Do PLC->Connect. Hit the Rescan for New PLCs (if it didn't already do it when the dialog box came up). Double click on the <new PLC> whose PLC Serial # matches yours. You should be prompted for IP Settings. Enter the previous settings.

Your existing Comm Link should be tied to that IP Address, so that Comm Link should now work (but the PLC is cleared).

I would ensure communications is working well before writing a project. After clearing your PLC and reconfiguring the IP address settings, double click on the Comm Link (not the Disk Project) and bring up a trend view that shows DST1 through DST4. These are all PLC scan time values in microseconds. Make sure the Comm Status is good (PLC->Link Info). You should not see any timeouts.

If everything looks good, go ahead and open the .dmd project file. Go ahead and try to Write the Project to the PLC.

Let us know your status (good, bad, ugly).