Atualizei um de nossos sites e foi agraciado com este erro:

=== Pre-bind state information ===
LOG: User = NT AUTHORITY\NETWORK SERVICE
LOG: DisplayName = <assembly>, Version=2.0.42.64, Culture=neutral, PublicKeyToken=c445f6f924945bd1
(Fully-specified)
LOG: Appbase = file:///E:/Web/
LOG: Initial PrivatePath = E:\Web\bin
Calling assembly : <assembly>, Version=2.0.42.67, Culture=neutral, PublicKeyToken=c445f6f924945bd1.
===
LOG: This bind starts in default load context.
LOG: Using application configuration file: E:\Web\web.config
LOG: Using host configuration file: C:\Windows\Microsoft.NET\Framework\v2.0.50727\Aspnet.config
LOG: Using machine configuration file from C:\Windows\Microsoft.NET\Framework\v2.0.50727\config\machine.config.
LOG: Post-policy reference: <assembly>, Version=2.0.42.64, Culture=neutral, PublicKeyToken=c445f6f924945bd1
LOG: Attempting download of new URL file:///C:/Windows/Microsoft.NET/Framework/v2.0.50727/Temporary ASP.NET Files/root/5ee48cb7/31fcfc81/<assembly>.DLL.
LOG: Attempting download of new URL file:///C:/Windows/Microsoft.NET/Framework/v2.0.50727/Temporary ASP.NET Files/root/5ee48cb7/31fcfc81/<assembly>/<assembly>.DLL.
LOG: Attempting download of new URL file:///E:/Web/bin/<assembly>.DLL.
WRN: Comparing the assembly name resulted in the mismatch: Revision Number
ERR: Failed to complete setup of assembly (hr = 0x80131040). Probing terminated.

Onde<assembly> é o nome da montagem.

Se eu li isso corretamente, a montagem (.67) está tentando carregar a si mesma, mas a anterior (.64) e está falhando porque, obviamente, um arquivo não pode ter 2 versões ...

O que pode causar esse problema? É minha configuração ou a compilação do assembly que está errada?