I am trying to checkout a repository on my windows machine. i am getting the following error.

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As Matteo have pointed out, the error is for denial of access. you will have to provide the username and password. And you should have read access for that user.
Problem you have said that it is not asking for credentials. For this one work around is that to clear saved data for credentials.
Got to TortoiseSVS->Settings->Saved Data -> Authentication Data-> Clear
Then try to access the repository. It will ask for credentials.