无法将对象强制转换为自己的类型

Unable to set property 'Model' on object of type 'CSBApp.ExtHdr'. 
The error was: [A]TQ.ModelExt cannot be cast to [B]TQ.ModelExt. 
Type A originates from 'TQ.Exts, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' in the context 'Default' 
at location 'C:\_work\Server.SSB\bin\Debug\net5.0-windows\TQ.Exts.dll'. 
Type B originates from 'TQ.Exts, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' in the context 'Default' 
at location 'C:\_work\Server.SSB\bin\Debug\net5.0-windows\TQ.Exts.dll'.

好像加载了两个相同的程序集!

object Model = ...; // actually a ModelExt
var a1 = Model.GetType().Assembly;
var a2 = typeof(ModelExt).Assembly;
if (a1 != a2) {
    DBG.Log("merde...");
}

组件,a1和;a2,具有相同的名称、版本和;位置不同,但m\ U组件不同。

这怎么可能??