Rouf,
can you check the ArcGIS Server logs to see if there are any error messages returned for this failure to enable feature access extension?
Hope the Map does not include any of the following datasets which are not supported in a feature service. At 10.0 final Service will be created, but any of these unsupported layers will be dropped. there could be issues in pre-release version where the service creation may fail with Maps containing some of this unsupported data.
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The following data types are not supported in feature services; annotation, dimensions, terrains, raster datasets, attributed relationship classes and many-to-many relationship classes.
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Thanks
Ravi