Error -26609: HTTP Status-Code=503 (Service Unavailable) for "http://My_Application.aspx"

Hi, 

i'm using LR 11.0 on windows 7 64 bit.

How to resolve this error:-  Action.c(17): Error -26609: HTTP Status-Code=503 (Service Unavailable) for "http://My_Application.aspx"

whenever i run my scenario through HP LoadRunner Controler then this error displayed in Scenario Status -> Errors window

what are the causes behind this error?

please help me to reslove this issue