I can install via gacutil, but not uninstall the same dll

Question

I have installed a DLL using the gacutil.

gacutil.exe /i SI.ArchiveService.CommonLogic.Exceptions.dll

Using the gacutil /l shows that it is indeed installed.

SI.ArchiveService.CommonLogic.Exceptions, Version=1.0.0.0, Culture=neutral, PublicKeyToken=925c8734ae397609, processorArchitecture=MSIL

Then I wanted to uninstall it.

gacutil.exe /u SI.ArchiveService.CommonLogic.Exceptions.dll
Microsoft (R) .NET Global Assembly Cache Utility.  Version 3.5.30729.1
Copyright (c) Microsoft Corporation.  All rights reserved.

No assemblies found matching: SI.ArchiveService.CommonLogic.Exceptions.dll
Number of assemblies uninstalled = 0
Number of failures = 0

Why doesn't this work? How do I uninstall it?