A little more precision:

The output is :
v-------------------------------------v
C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Microsoft.Common.targets(558,9):
error MSB4057: The target "PostBuildEvent" does not exist in The
project.
^-------------------------------------^

And in the error window, the error is:
v-------------------------------------v
The target "PostBuildEvent" does not exist in The project.
^-------------------------------------^

The error is located in the module "Microsoft.Common.Targets" on the
line starting with "DependsOnTargets":
v-------------------------------------v
   <Target
       Name="CoreBuild"
       DependsOnTargets="$(CoreBuildDependsOn)">

       <OnError ExecuteTargets="_TimeStampAfterCompile;PostBuildEvent"
Condition="'$(RunPostBuildEvent)'=='Always' or
'$(RunPostBuildEvent)'=='OnOutputUpdated'"/>
       <OnError ExecuteTargets="_CleanRecordFileWrites"/>

   </Target>
^-------------------------------------^

Note that the builds events are empty.

I try the following steps, but this stupid error is still there:

- I reinstalled VS2005
- I tried to rebuild one of my existing project,
- I created an empty project

This last case seems to tell me that something is wrong in the VS2005
installation: but I reinstalled (repaired) all from the original disks.