# The Web Connector shows an unhandled error
Source: https://www.desktopaccountingapi.com/docs/help/connection-errors/web-connector-unhandled-error/

> Fix a Microsoft .NET error window in the QuickBooks Web Connector, such as "Index (zero based) must be greater than or equal to zero", when you add a connector file or close the Web Connector.

The Web Connector itself sometimes stops with an error window from Microsoft .NET, the software it is built on. This is a problem inside the Web Connector, not in your company file, and it does not change your QuickBooks data. Restarting the Web Connector clears it.

## What you see

A window with technical text appears over the Web Connector. It may say an unhandled exception has occurred, and show a message such as:

> Index (zero based) must be greater than or equal to zero and less than the size of the argument list.

Other messages you may see include "Object reference not set to an instance of an object" or "Cannot set Visibility to Visible or call Show, ShowDialog, Close … while a Window is closing." The window may have **Continue**, **Quit** or **Details** buttons. After it appears, the Web Connector may stop responding, and **Exit** may do nothing.

## Why it happens

The most common time is when you add a connector file (`.qwc`) while the Web Connector is in the middle of an update for another app in its list. The Web Connector can trip over itself while it saves the new app and runs the other one at the same time.

It can also happen when you close or restore the Web Connector window while it is busy.

## How to fix it

1. **Close the error window.** Click **Continue** if there is one, or close the window.
2. **Exit the Web Connector.** Choose **File › Exit**, or right-click its icon near the clock and choose **Exit**.
3. **If it does not close within a minute,** open Task Manager (**Ctrl+Shift+Esc**), select **QuickBooks Web Connector** (`QBWebConnector.exe`) and choose **End task**. End only the Web Connector, never QuickBooks.
4. **Start the Web Connector again** from the Windows Start menu.
5. **Look for the app's row.** If it is there, leave it. It checks in again within about 10 seconds. If you were adding the connector file and the row is missing, continue with the next step.
6. **Add the connector file again when no update is running.** Wait until no row in the Web Connector shows an update in progress. If other apps update often, uncheck **Auto-Run** for them for a moment. Open the connector file again, then check **Auto-Run** for the other apps again when you are done.

Never end QuickBooks (`QBW.EXE` or `QBW32.EXE`) in Task Manager. It may be writing to the company file, and ending it can damage the file.

If QuickBooks says the company file is being used by another application after you ended the Web Connector, see [QuickBooks says the company file is being used by another application](https://www.desktopaccountingapi.com/docs/help/connection-errors/company-file-in-use/). QuickBooks lets go of the file by itself after a few minutes.

## How to avoid it

- Add a connector file only while no update is running in the Web Connector.
- Close the Web Connector with **Exit** only when no update is running.

## How to check it worked

The Web Connector opens without an error window. The app's row updates within about 10 seconds and shows no error in **Last Result**. If you were in the middle of setup, the setup page passes **Web Connector checked in**.

## When to contact the app's support

Contact them if the error comes back every time you start the Web Connector. Send the time, the exact text of the error window, a screenshot of the Web Connector window with every row visible, and the Web Connector log file, `C:\ProgramData\Intuit\QBWebConnector\log\QWCLog.txt`.

## Related pages

- [Another update is in progress](https://www.desktopaccountingapi.com/docs/help/connection-errors/another-update-in-progress/)
- [QBWC1039: Unique OwnerID/FileID pair value required](https://www.desktopaccountingapi.com/docs/help/connection-errors/unique-ownerid-fileid/)
- [Upgrade the Web Connector](https://www.desktopaccountingapi.com/docs/help/guides/upgrade-web-connector/)

For developers, see [`INTEGRATION_CONNECTION_NOT_ACTIVE`](https://www.desktopaccountingapi.com/docs/errors/#integration_connection_not_active).