HTTP 502 Proxy Error While accessing Cisco ASDM

Are you getting the following error while accessing ASDM from your Client machine that is behind your corporate Firewal (TMG-2010)?
Unable to Launch ASDM from 172.16.1.1 (IP Address)
Unable to tunnel through proxy. Proxy returns “HTTP/1.1 502 Proxy Erro (Forefron TMG denied the specified Uniform Resource Locator (URL).”
So the actual restriction is in TMG 2010 and the connection is denied to the ASDM by TMG Default Rule, if your TMG Firewall is not configured to to access internal/external IP at which that ASA/PIX ASDM resides.
Suppose if your ASA/PIX firewall is on internal/inside network and in TMG you have created Web Access Rules so that it only allows connections from Internal to External Networks than connection from your Internal Clients to ASA/PIX can be denied by Default Web Access Rule of TMG 2010.
Either you can allow from Internal to Internal+External or You need to put exception in Allow Web access rule so that the connection from your internal networks is allowed.
Allowing all connections from internal to all internal and external networks is simpler, here I tell you how to put exceptions if your company doesn’t wants allow all connections.
For putting exception, you need to create a URL Set and Put it in allowed Exception Ruel.
Right Click Allow Web Access Rule > Properties > Select tab TO > Click ADD > Click URL Set > Click New
In the New URL Set Windows create the URL set as shown in the snap Below and give it any name, I Named it ASDM, when finished Click OK.
Once the URL Set is Created, Click Add Button to add this URL Set into the allowed destinations box.
Click OK and Apply the Changes in TMG and and Play with ASDM error Free.
Please mention if this worked for you..

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