Nitin,
I think we will need an account/profile and steps to reproduce this.
However, looking in one of your profiles and checking the tag mappings for the CoreMetrics tag, I don't see anything mapped to "ManualImpressionTag_cm_sp." You've got to make sure that you're not only sending 'impression_cm_sp' in the utag.view or utag.link function, but you also have it mapped properly using the Mapping Toolbox within the CoreMetrics tag.
Also, when you trigger your utag.view or utag.link function make sure you are populating 'page_id' in addition to 'impression_cm_sp.'The 'page_id' variable is populating the Page ID value in the Impression tracking server call, which is required. You're utag.view/utag.link would need to include both like so:
utag.view({page_id:"some page id",impression_cm_sp:'some impression'});
You can populate more than the above, but that would be the minimum.