Single ASP.Net User Control compiled in two assemblies? How is this possible ?

Hi,
We have a web application (not a web site) with several web user controls (not web custom control).
It builds fine but when running, we always eventually get a error like this one :

Exception information:      Exception type: HttpCompileException      Exception message: c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\piolnonlifeonline\97fa7039\95b6e631\App_Web_fwolnonlifeonlineprintpreviewview_fffn.aspx.cdcab7d2.z9j75n_j.0.cs(2948): error CS0433: The type 'ASP.uwolnonlifeonlinecontantepremie_ascx' exists ...