Unchecking "Enable Just My Code" may uncheck the "break on all exceptions" stuff.

Going to: DEBUG > Options and Settings... ...brings up the "Options" dialog box wherein going to: Debugging > General > Enable Just My Code ...one may find this checkbox. One should then doublecheck that at: DEBUG > Exceptions... ...all of the checkboxes have not become unchecked. You may wish to recheck them. When a DotNetNuke application fails to spin up and throws an opaque, unhelpful error unchecking "Enable Just My Code" and then doing the "break on all exceptions" trick might be a good way to figure out where the application is blowing up.