Generally there are 2 types of RPMs, "regular" ones and "source" RPMs. Source RPMs actually contain the original source code for the package you are installing. The "rpmbuild" command first compiles the source files and then installs the resulting executable files in the correct directories. Most source RPMs have ".src." in the filename and can only be installed using the "rpmbuild" command. See the example below.
Sample source RPM filename = tac_plus-4.0.3-2.src.rpm
Regular RPM files can only be installed with the "rpm" command. Regular RPMs don't have the ".src." in their filenames and contain pre-compiled executable files. The rpm command just installes them in the correct directories.
Sample regular RPM filename = tac_plus-4.0.3-2.i386.rpm
You are most likely getting the error because you are attempting to install a regular RPM with the "rpmbuild" command instead of the "rpm" command.