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

Fix: QuickBooks Error Code 1603. The error code 1603 typically appears when users are either trying to install or to update QuickBooks. This is quite a big problem since QuickBooks needs to stay updated if you want to keep in touch with the latest tax files, especially if you just entered a new year.
TxnTaxDetail not allowed when GlobalTaxCalculation is set to NotApplicable. You can only nest 5 levels deep. Subscription period has ended or canceled or there was a billing problem. See QuickBooks Online subscriptionstates for further information.

Locate Quickbooks in Control Panel or Settings and click on Uninstall. QuickBooks’ uninstall wizard should open with two options: Repair and Remove. Select Remove and click Next in order to uninstall the program. A message will pop up asking “Do you want to completely remove QuickBooks for Windows?”

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