Web Part Page Error prevents opening it for update

When an error occurs after editing a web part page, for example by adding a custom WP, sometimes you can't access the page anymore and therefore you can't to fix the problem by removing that WP.

Although not well documented, there is a solution to this issue. You just need to add the suffix ?contents=1 to the page's URL. This will present the maintenance area of that page. In the maintenance page you can exclude the WP and view the page again.

For example, if your URL is www.myDomain/mySubSite/myPage.aspx, it should look like:
www.myDomain/mySubSite/myPage.aspx?contents=1.