I got some more complete uninstall instructions from Paya for an issue with repeating notices from Paya, not a lack of communication: 

1. Open the Control Panel and in the Programs and Features Menu
2. Right-click on Sage Exchange and Select the option to Uninstall Sage Exchange
3. Open the "Start Menu"
4. Paste "C:\ProgramFiles (x86)" (without the quotes)
5. Delete the "Sage Payment Solutions" folder
6. Paste "C:\Users\%USERNAME%\AppData\Local\" (without the quotes)
7. Delete the "Sage Payment Solutions" folder
8. Paste "C:\ProgramData"  without the quotes
9. Delete the "Sage Payment Solutions" folder
10. Download the latest version of the Sage Exchange Desktop Bootstrapper from https://www.sageexchange.com/install/#/sedv2x/en
11. Extract and run SageExchangeDesktopBootstrapper.exe 
12. Navigate to the SageExchangeDesktopBootstrapper.exe file
13. Right-click and Run as Administrator
14. Follow installation steps

Maybe you have already done that, but those extra folders did seem to persist and when deleted the troubles stopped.  On another issue, I could not get Paya to open nor Excel to open.  Paya offered to have a conference call with Sage support because they suspected a corrupted msi file in Sage was causing a communication breakdown. 

For Excel not opening, I was working on stuff that my IT guy said was deep in the bowels of Windows where no human should be trekking.  He said when you get to that point, it might be easier to call Uncle and start over.  We re-installed Windows, Sage and Excel and a lot of our grief was eliminated and the workstation went back to being productive. 

Good luck,

Chris

Yes, I think we went through these steps. The problem with this issue is that several people, including myself, have noticed that Sage and Paya appear to absolve themselves of responsibility. I don't dispute that this is likely environmental and specific to a workstation configuration. The next question from 101% of my customers is "ok, so tell me what I need to do to fix it."

IMO, reinstalling either Sage or Windows is not an acceptable solution.

I typically do a similar process as Beevet, and that often resolves it.

Same here. Out of 100 times seeing this type of error message - 98 times an uninstall and reinstall works.

Just resolved this for a client. I had sent them the KB, but they had trouble finding the "C:\Users\%USERNAME%\AppData\Local\" folder and the  "C:\ProgramData" folder was hidden.

IMHO, it’s a lot for a typical user to digest, although I have to think any IT admin worth his salt would be fine with it.

Another aspect that makes this a burdensome task is that reinstalling Paya requires quite a bit of patience:
1. Downloading and running the executable.
2. Always receiving a pop-up message saying that there is an update needed (see below).
3. Then we sometimes see a message in the System Tray that another update is needed (didn't get a shot of that one - next time).

The Windows/Sage/Office reinstall is not an acceptable solution, but the other solutions we see when things get to that level are not acceptable either.  Repurposing the computer as an artificial reef in our local creek or as a window breaker or as the center of stress relief at the company picnic (think of the printer in Office Space) were alternatives we discussed colorfully at length.  

I see a very small portion of the world and have to make decisions at that level.  I appreciate guys like you that see a broader picture and have the ear of the software developers and can get fixes and improvements made on the broader level.  These improvements you insist on tend to help us little folk.  

Chris

fyi; in case the min. requirements may be the issue. 

fyi; in case the min. requirements may be the issue. 

This issue has now affected one of the clients we work with. It began with the recent update for Paya. It is affecting two computers out  of ten. We reviewed the notes above, following suggestions with no success. Anyone have any update on this?

Nothing to update. We've tried to uninstall/reinstall as noted above, and on a couple of workstations, we have not been able to make it work. The customer could reinstall a lower version, and that reportedly worked. They cannot update a few of their workstations.

I'm still actively looking for some type of resolution. Admittedly this seems to be environmental. We just haven't been able to pin down exactly what needs to change.

Win 7 workstations might not have TLS 1.2 installed.

Wayne, 
Is this still unresolved, do you have an open case with support?  The message Unable to communicate with Sage Exchange is generic and could be almost anything.  Since it is just a couple workstation and being on 100 Advance, you are correct for this being environmental especially if it works from other workstations. Solution for one workstation may not work for the next.  Just like you said 98 of 100 reinstalls has worked.
Email me the case info if there is one and I will take a look.  If no case, email me the details and I can start one.  

Testing Sage 100 if communicating with Paya Connect Desktop (PCD)
Here is my process

1. . Right click the Paya icon in the system tray and select tracing and turn On.  
2. RIGHT click Paya icon again and Exit.  I shut it down on the workstation
3. In Sage I open AR Customer Maintenance select any customer, and go to Tab#2 Additional
4. Click the button Credit Cards / ACH or Alt+E to open the Customer Credit Card & ACH Payments Maintenance panel.  This should launch PCD and should be visible in the tray.  If not, there is an issue usually .NET failed during installation or during the automatic update prompt.  check log if anything shows in PCD.
5. If there is a message but it does show in tray, I continue with selecting a payment type and adding a Card to the Vault.  This confirms there is communication.
   
   NOTE:  Canceling during this process will generate that message Unable to communicate with Paya.  which is normal.

Ronnie,