The error message looks clear.
Maybe, what you need to do is to contact your local distributor and get the updated ECP file for your standalone ArcGIS Image Server 10, and then license it. If successful, please register it again!
On ESRI advices, however, you may have Image extension installed rather than standalone ArcGIS Image Server 10, after ArcGIS Server 10 is setup, except that you are users of standalone ArcGIS Image Server 9.3/9.3.1. The standalone ArcGIS Image Server 10 is only used for smooth transition (the standalone ArcGIS Image Server 10 is last and final release from ESRI). That is, you can keep using old image service defination files as image services and also publish those files (similar to mosaic datasets) to ArcGIS Server 10 with Image extension as image services.
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Personally, it may be good strategy to keep improving this standalone ArcGIS Image Server in order to keep using image service definition files (that is, as a permanent/separate product), at least, in next 3-5 years. For example, to support more infrastructures like cluster server, easily register with ArcGIS Server 9.3/9.3.1 or 10 on Linux & Unix (as separate image extension), easily update, and develop more client add-on applications for oil and engineering applications. If so, ESRI may have more market shares in imagery serving aspect, compared to only selling the integrated ArcGIS Server 10 or higher with image extension because, we (maybe, including non-ESRI users) do see many benefits from standalone ArcGIS Image Server like flexibility and good performance.
Of course, other users still may have a choice to use ArcGIS Server 10 with image extension directly for Mosaic Datasets, even, use both standalone ArcGIS Image Server and ArcGIS Server with Image extension for different applications / end users in large organizations.
