Hello Scott, Thank you for the reply. I don't use it in the code, just declare it in the way (declaration, usage): ------------------------------------------ Register Src="../common/WebUserControl.ascx" TagName="WebUserControl" TagPrefix="uc1" ... uc1:WebUserControl ID="WebUserControl1" runat="server" ------------------------------------------- (I removed some symbols to make the code appear). I also tried to include "Reference" directive at the page top, but that didn't work. Everything works when I compile the application, even when I launch it from Visual Studio (Shift+F5). This is the point where a hidden reef begins. When I precompiled the project (updatable), the page gives the error. I made several experiments and if I put the control into the same folder, where the page is, everything works ok. Also, I noticed that pages which are in the root can include any controls from "common" subfolder in the same way I described and it works. I.e. I understand that pages may include controls which are in "subfolders", and the problems occur when they include controls from parallel folders. I think this is due to the new compilation model, but maybe there is some workaround. I was searching the forum, but didn't find anything helpful, expect suggestions to use "Reference", which didn't help. Thanks. Ray.