When Zed Axis attempts to connect to QuickBooks or a QuickBooks company file you get an error message of "Unable to connect to QuickBooks" or "Please connect to a QuickBooks company file".

Please follow these steps to troubleshoot this issue:

Step One : Latest versions of QuickBooks and single installs

1. Ensure that you have QuickBooks installed, your company file open, and we recommend that you login to QuickBooks as the Administrator
2. Check that you meet the minimum systems requirements to use Zed Axis Zed Axis System Requirements.
3. If you are using Microsoft Vista, please ensure that you have User Account Control  (UAC) set to On, QuickBooks requires this to be set on and check that Zed Axis is running at the Admin permission level.

Step Two: Running multiple releases of QuickBooks on one machine
If you are running multiple releases of QuickBooks on the same machine ie (2007 & 2008, or Canada and UK) then you may have installed an older version after the latest release, if you have you will need to follow the instructions on this article to resolve this issue.

Step Three : Older versions of QuickBooks 
If you are using an older version of QuickBooks, (07/08 Australia & New Zealand, or 2007 UK) then you may not be able to connect to QuickBooks.  To correct this issue follow these steps:

1. Login to QuickBooks and your company file as Administrator in single user mode
2. Select the company preferences Edit > Preferences > Integrated Applications > Company Preferences
3. For each application listed we are going to uncheck the ability to login automatically:
   1. Highlight the application and click the Properties tab
   2. Un-check the box which says "Allow this application to login automatically".
4. Restart QuickBooks and reset the login automatically mode and a user with sufficient permissions
5. Login again as Administrator in single user mode
6. Select the company preferences Edit > Preferences > Integrated Applications > Company Preferences
7. For each application listed:
   1. Highlight the application and click the Properties tab
   2. Check the box which says "Allow this application to login automatically" and select a user with admin permissions
8. Restart QuickBooks.

Intuit Support have an alternative approach listed in here

Step 4: Determine if the issue is a corrupt QuickBooks interface or Zed Axis

1. Download, install and run the SDK Diagnosis Tool to determine if the problem is QuickBooks or a Axis issue.
   1. If you are unable to connect with the SDK Diagnosis Tool then it may be because you have multiple versions of QuickBooks installed on your computer, your interface files may have been overwritten, please follow these instructions to clean up your installation.
   2. If you are able to connect then it is a problem with Axis please raise a ticket with support quoting the version of QuickBooks that you are using and the error message you are receiving and we will endeavour to correct this as soon as possible.