Getting Error in subpanel display

[akkimca]

Hi all,

i m facing one interesting problem in the Product module in sugacrm 5.1..
My problem is that:
When i "Clear Vardefs Data Cache" than all the subpanels are display in in the Product module but when i go to Vendor module and return back in Product module than i get this error:
Here is the error:

Fatal error: Call to a member function getQuery() on a non-object in C:\xampp\htdocs\sugarcrm\data\SugarBean.php on line 2672

after doing "Clear Vardefs Data Cache" again, i get all subpanels..

so anyone tell me why this is happening ???