Most likely it is a problem with the Extension manager.
Try uninstalling the Extension manager for dreamweaver then reinstall it. also, rename the users configuration folder, for help locating the users configuration folder, see the common installation issues:
once you locate the configuration folder, rename it to something like configuration_back, then open Dreamweaver to recreate the configuration folder.
Then try installing the Deprecated server behaviors extension
for DW CC 2014:
for DW CC:
open dreamweaver and make sure the Window -> Server Behaviors, Data Base access point's exists.
Close Dreamweaver, then install Data Bridge, when you open Dreamweaver again, make sure the WebAssist installer completes, restart DW once it finishes.