Hello Ashhad,
If you are using  LR 11.04 then you do not  need the  ''uid='' part just this 
LR.getParam(''username'')       
Replace the Original values  ''username'' in the step's Argurment section  And  you'll need to create a parameter list in the Vugen for  the ''username''
      Question :  What LoadRunner patches  do you have installed???
To  check  open Vugen> Help> about ....  If you want to  use Ajax Truclient  and the  have the Ajax Truclient  Help  Documents you  MUST have LR 11.03 or LR.04
*******Best way to Parameterize a  value do this:*********
	1. Recorded your Script
	2. Find the step you want to parameterize Press the  expend step  arrow (right side)
	3. Open the ''Arguments'' subsection to see your Value
	4. Highlight EVERYTHING in the Value box, (yes  the '' '' too)
	5. Right Click on the highlighted  Value and select ''Replace with a Parameter''
	6. The ''Enter Parameter Name''   popup will appear
	7. Change the ''Parameter Name''
	8. Press ''OK'' (this Bring the Vugen to the front)
	9. Press the ''parameter properties'' icon
	10. Add and Adjust Parameter as needed
	11. Press ''Close''
	12. Note the Value is now [  LR.getParam(''USER_ID'' ]
	13. TO  check the code  move the mouse to the  right of the Values: Box  and click on the JS when it  appears
	14. Press OK