Often this will happen if you have accidentally downloaded an incomplete page or a corrupt cookie. In that case, clearing your browser cache/cookies should resolve the issue.
It can also happen if you assign a role to a user that conflicts with a more powerful role they have. The following roles can limit a user's capabilities and cause conflicts for user accounts:
Cataloging Basic
Cataloging Simplified
Cataloging Limited
Cataloging Evaluation - This is no longer used and should never be assigned.
WorldShare ILL Partner
There is more information about roles that are available in Worldshare.