Last time I had this happen it was because the reference was to the wrong px.dbservices I would remove the reference and readd it from the bin folder of your current instance.

Thanks, @Shawn Burt I have already done this. I even removed all references and added all again but no luck.

Sorry. I am not by a computer to check this out further tonight. I will check in the morning.

Appreciated @Shawn Burt 

I am rebooting my IIS and clearing temp files and caches … it might also help. If I find something I will post an update here

I did some cleanups and resets and restarts and fixed it somehow. I am not sure what was the root cause. It just wanted to drive me crazy. 

I have had the asp.net temporary files get “stuck” with a specific dll and not be able to unload the dll to allow it to be updated so it keeps generating an error similar to yours. reboot typically fixes it. Glad things are resolved :)