I get this error when trying to export clips that I've cut that are in my timeline in Premiere CS4, which IS activated. The funny thing is that in Premiere, it looks like it works. It's only when I notice, hey, there's a new thing in my taskbar and see this message. However, the clips do NOT export.
AMT Subsystem Error
Thank you for using Adobe Media Encoder CS4. The Adobe product that installed Media Encoder has not activated.
Please launch and activate that Adobe product before continuing to use Media Encoder.