The idea behind the var_dump line was that you would do whatever you did before to produce the message in the first post, then immediately before that the page should print out the value of $value which may tell us something.
Anyway it looks like something else has happened, so the generic debug routine is to deactivate all plugins, rename the plugins folded if necessary, then pick the default theme. If it works now, put things back one by one and test to try to identify the element that's causing the problem.
Ensure your theme is up-to-date.