IP Address Issue

I was create a reseller account my WHM server and was given a Share IP . Now I modified that account as a normal hosting account. I have been change site IP address and assign another share IP. Now I want to use that reseller shared IP for another domain dedicated IP. When I try to give that IP to another domain I see (Shared by No body ) and when I try assign IP I see Sorry, . . . . (IP) is in use by another domain name and is not a shared ip.