Please try below steps,
- It seems an IE regression. Please try this fix by Microsoft Update:
http://support2.microsoft.com/default.aspx?scid=kb;en-us;3025390
2. If still dint work,
It seems that this issue occurs after Microsoft security patch for Internet Explorer.
We found out that the "compatibility View" list was cleaned and got empty.In order to fix it, you need to add again the site to the compatibility view list.