<h3>Image Assist &amp; ImageField Assist</h3>
Under certain conditions these modules can block access to the header input section of the admin.
They need to be disabled on certain views paths. To do this go to
Image assist ->Access settings
check "NOT on specific paths":
and enter

Drupal 7.x has different paths
admin/structure/views/ajax/display/*
admin/structure/views/ajax/*
For futher reference please see <a href="http://drupal.org/node/415990">this issue for more information</a>