Below are the troubleshooting steps recommended for the error "Page Unavailable" or "Server Error in '/' Application.":

1. Stop and then restart all the services in a specific order based on the knowledge base article below.
http://support.waspbarcode.com/kb/articles/cloud-on-premise-stop-and-restart-all-services-bounce

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2. Run Wasp Configuration Tool as Administrator, log in with Windows Authentication.
C:\Program Files\Wasp Barcode Technologies\Wasp On-Premises Software\License\configure\Wasp.Installer.Configure.exe
Then open the Wasp Config Tool as admin
select Windows Authentication
Validate the Config and Auth database connections
Update the Writer and Reader passwords: (if there are any errors here, just keep trying until it says "OK")
username: dbo_Writer, password: db0-Wr1ter_P455w0rd
username: dbo_Reader, password: db0_Re4der-P455w0rd
Then save.

Validate all the other tabs (where there is a validate button) from top to bottom, (or left to right for older versions). Note that this utility is used for multiple products (AssetCloud, InventoryCloud, PreciseTime), so the tabs for products you don't have are expected to have blank fields.

If any of the tabs throw an error, try to validate a few more times (sometimes it's just waiting for certain components to start back up after the bounce)
If it keeps failing after 3+ attempts, go back to Step 1 to bounce everything, and try to validate that tab once more.
If it will not get past those errors, you may need to troubleshoot this in IIS to determine why that site/service is not working as expected.
(The most common reason for a failure at this point is port conflicts)
Once all the tabs have been validated, save and exit the config tool*

With validation complete, proceed to step 3.

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3. Stop and then restart all the services again, same as in step 1. Then attempt to open the software again.