migrating java1.5 gives error.

i have changed java 1.4 to java 1.5.and there is comiler error inconstructor HttpClient(url, null, -1); is ambigious.
Why it is giving this error.
Thanks.

i thinks this error due to same method used again with same parameters
HttpClient(url, null, -1);

I cahnged the method as httpClient(url,(String)null,-1); now ther is no compiler error.i guess java 1.5 is more restrictive about casting.
Thanks for your reply