Troubleshooting

Add-in Could Not Be Started

This add-in could not be started. 
Close this dialog to ignore the problem or click "Restart" to try again 

Check that the manifest file is valid and has all the correct tags.
Switch on the runtime logging to generate a log file.
link - docs.microsoft.com/en-us/office/dev/add-ins/testing/runtime-logging
link - stackoverflow.com/questions/58922052/excel-custom-functions-suddenly-stopped-working-on-local

Error installing functions

Error installing functions 
One or more add-ins failed to install or load custom functions 

Check the manifest file and all the referenced files.

Custom UI Runtime Error in trustedlocation

Custom UI Runtime Error in trustedlocation 
An error occurred while calling the callback: 'OsfIsVisible'  

Can't open this add-in from localhost

We can't open this add-in from localhost  
Click 'see details' for more information 

link - docs.microsoft.com/en-us/office/troubleshoot/error-messages/cannot-open-add-in-from-localhost
Check that the localhost URL is correct in the manifest file
Check that the port or http is correct.
Check that the webpack-dev-server is running.
Delete the Office Cache and replace the GUID with a new GUID

Office' is undefined

Javascript runtime error: 'Office' is undefined  
Office.js has not fully loaded. 
Your add-in must call 'Office.onReady' as part of its loading sequence or set the Office.initialize function.  

This could be a problem with a previous file being cached, try renaming the files.
Open the Command Prompt and run the followng to add a local loopback exemption.
CheckNetIsolation LoopbackExempt -a -n="microsoft.win32webviewhost_cw5n1h2txyewy"

Office.js is outside of Office client

Warning : Office.js is outside of Office client 

Internet Explorer, Advanced

allow active content to run in files on my computer - removes annoying prompt/message

A problem occurred while trying to reach this add-in

This can be caused by a URL file that cannot be found

JavaScript runtime error: '$' is undefined

Unhandled exception at line ?, column ? in https://localhost:MyFile.js 
0x800a1391 - JavaScript runtime error: '$' is undefined  

This means that the JQuery referred URL is not correct, check the relative path

ScriptedSandbox64.exe has stopped working

This add-in is no longer available

This add-in is no longer available: 
add-ins inserted during development are only available during debugging from Visual Studio. 

Incorrect host, host:Name = "Workbook2"
resid missing in the Resources
two resids are the same
function curly brackets has a missing semicolon

Addin not working correctly

Try turning on script debugging in Internet Explorer
Tools > Internet Options > Advanced
Under Browsing, uncheck "Disable script debugging (IE)" and "Disable script debugging (other)"
Remember to check them when finished

The Breakpoint will not be currently hit

If you right click on your task pane and press "Reload" you will not longer be able to hit any breakpoints.
If you hover over a breakpoint you will see the following tooltip
"The breakpoint will not currently be hit. No symbols have been loaded for this document"
You can add a button onlick event at the bottom of the task pane

<button onclick="window.location.reload()"> 
Reload Page 
</button> 

We cannot start this add-in because it isn't set up properly

Problem with the manifest (VersionOverides)

There were deployment errors. Continue?

Request for the permission of type 'FileIOPermission'

"Request for the permission of type 'System.Security.Permissions.FileIOPermission, mscorlib, version 4.0.0.0"
unblock any additional schemas
close and reopen Visual Studio

Access is Denied

This is caused when you try and access a http URL
The application runs as https
Task pane drop-down menu - security info displays the URL
It is best to keep your protocols independent by removing the prefix and just use a double slash prefix //myurl

Task Pane - Navigation to the webpage was cancelled

This appears when your web page is not being hosted on a https
Press "Refresh the Page"
You then see a message that says "This site is not secure"
Click "More information"
Your PC doesn't trust this website security certificate
Error Code: DLG_FLAGS_INVALID_CA

Add-in Error

This add-in is no longer available: add-ins inserted during development are only available during debugging from Visual Studio.
Please open your project in Visual Studio and re-run your application or deploy your add-in into a valid catalog and re-insert

Outlook - Unable to launch the IIS Express Web Server

Failed to register URL "http://localhost:44300/" for site 'OutlookAddin1' application "/".
Error description: cannot create a file when that file already exists

App error: Catalog could not be reached

Check the firewall settings because Catalog refers to the Office store.
Unable to access the Office Store

App error: This app could not be started

This app could not be started. Close this dialog to ignore the problem or click 'Restart' to try again   

Check that the latest Office updates are installed
Download the latest update for Office 2013

Object doesn't support property or method "??"

Check that Internet Explorer is not running in Compatibility Mode
Tools > Compatibility View Settings

Sorry we cannot load the app

Sorry we cannot load the app because your browser version is not supported 

Check you have a browser that supports HTML5 local storage and/or reset your Internet Explorer settings

The simpleType/complexType has already been declared

The simpleType 'http://schemas.microsoft.com/office/appforoffice/1.1:LongString" has already been declared.   

This is a schema validation error
Close all files
Double click on the manifest.xml file
Show Properties and select Schemas