It bothers me a few days the problem was finally solved. 
To summarize this issue, share out. It might be useful to other people.
The problem is this, I developed a workflow based WorkFlow sharepoint document library events, because the development is the use of a computer winxp, and sharepoint is on another computer, to the dll workflow portion opposed to the computer where SharePoint the GAC. I am using windows explorer directly onto the SharePoint server where the GAC folder. Other events enabled SharePoint document libraries and set the theme is not here, skip here. Fires when using the Document Library event, nothing happens, window event log: You can not instantiate an event handler .......
Analysis: Because I use My Network Places to dll directly onto the server's GAC, seen in the GAC have WorkFlow.dll registration, view the properties found "base code" line points to the My Network Places address. I will Dll copied to the server's local hard disk, and then drag it back into the GAC, and then after some agonizing, the problem is solved.
So I guess the GAC dll registration, storage is only a reference to assembly, the actual call or use the "base code" pointing dll. And I always thought dll is stored directly in the GAC directory. I can not access sharepoint dll registered at runtime, so the tips can not be instantiated. Later in the registration assembly to the GAC, it must first be copied to a local, re-registration.
In addition, Sharepoint assembly to the GAC seems to have a cache, I covered the GAC assembly, then IISRESET no effect if the original wrong thing or wrong. Only delete the GAC assembly, then IISreset, and then specify the SPS document library event handler to determine the place, Sharepoint will complain, this time a new assembly and then drag the GAC, the program runs on the right. I do not know if this is real. .
The above summary of my real problem, if wrong, but also hope my dear friend pointing.
Reproduced in: https: //www.cnblogs.com/baoposhou/archive/2006/01/20/321011.html