According to Intuit, Error Code 16026 can occur when a user is upgrading QuickBooks. There are several causes for this error:
- your internet connection is unavailable or has been lost
- your version of Microsoft Internet Explorer is not 5.5 or later
- your Microsoft Internet Explorer cipher strength (a security measure) is not 128 bit or greater
- some QuickBooks program files were not correctly installed or have become corrupted
- you’re attempting to run a version of QuickBooks prior to 2007 on Microsoft Windows Vista
Because this error code appears under very different circumstances, it’s helpful to rule out 1 or more possibilities to move closer to a solution.
Microsoft Windows Vista disables weak ciphers by default. If you’re running Windows Vista, your cipher strength is 128 bit or greater. Vista also installs a version of Internet Explorer newer than 5.5. Therefore, unless you’ve managed to modify your cipher strength or replaced Internet Explorer with an older version, these possibilities can be ruled out for Vista users. You can confirm your Internet Explorer version and cipher strength on the Help->About Internet Explorer menu choice. An example of Internet Explorer 7 running on Vista Ultimate is shown below:
Vista users may encounter this error when attempting to install a QuickBooks version that is not Vista compatible. QuickBooks 2007 and Enterprise Solutions 7.0 and later versions are Vista compatible. If you’re upgrading from a non-Vista compatible version (e. g., QuickBooks 2006) to a compatible version (e. g., QuickBooks 2009), it may be the case that your older, incompatible version is triggering the error. As a precaution, uninstall all prior versions of QuickBooks before installing the replacement QuickBooks 2009. After you’ve uninstalled the prior version of QuickBooks, restart your system. Be sure to have at least 1 complete backup of all data files and original program downloads or CD’s before performing any update or program uninstall. If you’re not sure you have a reliable and complete backup, stop and consult with a qualified professional before continuing.
If a prior, incompatible version of QuickBooks is not triggering the error when running Vista, another possible problem area to check is a corrupt program file. Uninstall the Vista compatible version of QuickBooks (e. g., QuickBooks 2009) and perform a fresh installation. Again, be sure to have at least 1 complete backup of all data files and original program downloads or CD’s before performing any update or program uninstall. If this also fails to stop the error code from appearing, it’s possible that the installation source (download or CD) is corrupt or that the files that the QuickBooks installer extracted have become corrupt. If you downloaded the program directly from Intuit, try downloading a fresh copy. Uninstall the last installation and attempt a new installation from the most recent download.
For more information on resolving Error Code 16026, consult this Intuit knowledge base article.