Add external assembly to plug in

I have to use external dll in my plugin (downloaded).

I have tried to merge the dlls by the next command line:

C:\Tools\ILMerge\ILMerge.exe /out:Merged2.dll  dll1.dll ddl2.dll

.Its worked

But, when I try to add keyfile in order to register my plugin by:

C:\Tools\ILMerge\ILMerge.exe /keyfile:key.snk /out:Merged2.dll  dll1.dll ddl2.dll

I get the next error:

Error 1 The command "C:\Tools\ILMerge\ILMerge.exe /keyfile:key1.snk /out:Merged.dll MOH.RichText.ConvertToImg.Plugin.dll NReco.ImageGenerator.dll" exited with code 1. MOH.RichText.ConvertToImg.Plugin

Thanks,

R.L.