You can fix the HP Printer Assistant error opening external application by doing the following troubleshooting.
1. Uninstall your HP Printer Driver from the Root Level and then reinstall it
How to Uninstall HP Printer from Its Root Level and then Reinstall it
Follow the steps below to uninstall your HP printer from its root level and then reinstall it:
Step 1: Search “Programs and Features” on your Windows computer.
Step 2: Choose your printer.
Step 3: Click on “Uninstall”.
Step 4: Search for “Devices and Printers” on your computer and then click on the result to open it.
Step 5: Find and right-click on your printer from the list.
Step 6: Select “Remove Device” or “Delete”.
Step 7: Press the “Windows” and “R” keys on your keyboard at the same time to open “Run”.
Step 8: Type “printui.exe /s” in the dialog box.
Step 9: Click on “OK”.
Step 10: Click the tab labeled “Drivers”.
Step 11: Find and click on your printer.
Step 12: Click on “Remove”.
Step 13: Choose “OK”.
Step 14: Click on “Apply”
Step 15: Click on “OK”.
Step 16: Close the window, and then restart your computer.
Step 17: Go to the HP website and download the Full Feature Software of your HP printer.
Step 18: After downloading it, install it on your computer.
If this doesn’t work, try the next troubleshooting.
Uninstalling your printer driver from the root level and then reinstalling it will also fix the HP Printer Error 74899.
2. Create a New Admin Account before Uninstalling the Driver and Reinstalling the Driver
How to Create a New Admin Account
Follow these steps to create a new admin account:
Step 1: Click “Start” on your computer.
Step 2: Click on “Settings”.
Step 3: Click on “Accounts”.
Step 4: Click on “Family & other users”.
Step 5: Choose “I don’t have this person’s sign-in information” at the lower part of the screen.
Step 6: Choose “Add a user without a Microsoft account” at the lower part of the page that opens.
Step 7: Enter the following details Username, password, and password hint.
Step 8: Click on “Next”.
If your OS is Windows 10 or version 1803, or a later version, security questions can be added instead of a hint.
After creating the account, you need to make it an administrator by doing the following:
Step 1: Click “Start” on your computer.
Step 2: Click on “Settings”.
Step 3: Click on “Accounts”.
Step 4: Click on “Family & other users”.
Step 5: Choose “Change account type”.
Step 6: Choose “Administrator” under the option for “Account Type”.
Step 7: Click on “OK”.
Step 8: Restart your computer.
Step 9: Once it comes on, sign in using the new admin account you just created.
Step 10: Now, uninstall the driver using the steps we shared above before reinstalling the software.
Read this: HP Printer Errors and Solution [Detailed] to learn how to solve other HP printer errors.
3. Do a System Restore – HP Printer Assistant Error Opening External Application
If the above doesn’t work, you can try performing a system restore to fix the issue.
How to Perform System Restore
To perform a system restore, do these steps below:
Step 1: Click “Start”.
Step 2: Search for “System Restore”.
Step 3: From the search results, click on “System Restore”.
Step 4: Choose a Restore Point before the error first appeared.
