What does this mean "This is returning type from Url property extanded about Block option"? Are you using a Url property to select a block and then want to get the Content Reference to the block? Blocks are not routable, so to select a block you should use a Content Reference property, not  an Url.

To get a block's Content Reference you just cast it to IContent: ((IContent)theBlockData).ContentLink. But if you use a Content Reference property instead, then it's not needed since you already have that value in the property.