This is caused by you having a web page listed in the Documents section of your layouts: the browser built in to ConQuest is very basic and that causes this error to appear. It does not affect your Estimate at all.
To prevent this error from appearing, you will need to remove the web page in question:
Go to the Layouts menu and hover over Documents, the sub-menu should appear beside it.
Locate the web page in this list, right-click it and select None.
This will remove the document from your layout, and the error should not appear again. If you still get the error, then there may be a glitch which has prevented a web page from being fully removed: It will not display here, but will still be loading. Right-click every None in the list and choose None again. If the error persists after this, and you have documents such as PDFs listed, set those to None as well. Once the error has been cleared, you can add them back.
An error has occurred in the script on this page
I get a script error when starting ConQuest "Do you want to continue running scripts on this page"
Written by Alina Stepanek