How to FIx web part did not support connection or not allow authoring Connection

when i implmented a connection web part to allow two webpart talk to each other.

on the provider web part, there will be a dropdown list control to show a list of avaialbe option,

the consumer web part will display the detail of the selected option.

after i completed the development and deploy the project to the server. then i add these two web parts

to a  web part page. when i try to configure the connection between those two webparts. the connection

option is the popup windows had been grey out. i hover the mouse over the connections option. it show

that "the web part you are connected from does not allow authoring of connections"

When i edit the page in the sharepoint 2010 sharpeoint designer, i move the mouse focus on the control, then

right to show the popup menu. then i selected add connections, i got this error "the web part did not 

support connection"

I try to Google to find a solution, but it is not that helpful, after few hours investigation, i figure out the root cause of the error.

Though i added the web part by selecting the WebPart template under Sharepoint 2010 section, i thought it should automatically create a sharepoint webpart for me.
       public class ProviderWebPart : WebPart( actually referencing System.Web.UI.WebControls.WebParts.WebPart), IProject
    {

after i change it with absolute reference to sharepoint web part

public class ProviderWebPart : Microsoft.SharePoint.WebPartPages.WebPart, IProject
    {

then all the error is gone  and i can configure the connection.