dll 不能加入arcmap

在arcmap中     在进行 tools－customize－commands－add from file  操作的时候，为什么有的dll文件不能加入，包括有一些自带的例子的dll。 给出的提示是：没有对象加入。
我试着在vb中重新编译了一次，但是还是相同的提示，


<P>请问，怎么解决，谢谢了。</P>

<P>你可以查看帮助里，每个例子都有说明的，并不是每个例子都是直接add的，例如<b>Display Extension这个例子，他的使用方法说明是：</b></P><P><b>How to use:</b> </P><OL><LI>Register this sample's dll by compiling the sample or by using Regsvr32.exe. <LI>If using the Visual Basic sample use the Categories.exe program or the ESRI Compile and Register Add-in, to add the classes clsDragPan, clsFullExtent, clsPanDown, clsPanLeft, clsPanRight, clsPanUp, clsRedoExtents, clsUndoExtent, clsZoomIn, clsZoomOut and clsDisplayOptions in the 'ESRI Mx Commands" category. Add the clsExtension class to the 'ESRI Mx Extensions" category and the clsToolbar class to the 'ESRI Mx CommandBars' category. This will happen automatically if you are using the Visual CPP sample. <LI>Close and re-start ArcMap. <LI>On the View, Toolbars pulldown enable the Display Extensions Toolbar. <LI>Select the Tools, Extensions pulldown option and enable te Sample Display Extension. To enable the Raster Roam option you must also enable the Spatial Analyst extension. <LI>Enter the Zoom and Pan factors required and make use of the Zoom and Pan commands. </LI></OL>