[Evolution] Problem installing 1.5.6 RPM snapshots in Mandrake

[Andrew Conkling <andrewski verizon net>]

I'm trying to install the 200404121814 snapshots of Evolution 1.5.6 on my Mandrake 10.0 machine.  I know the 
RPMs are for 9.2; that shouldn't cause any problems.  (I successfully installed 1.5.5 last week.)  However, 
when installing the libgtkhtml3.1_7-3.1.11.0.200404121814-0.snap.ximian.7.1.i586.rpm package, I get the 
following error:

root:evo1.5.6$ urpmi libgtkhtml3.1_7-3.1.11.0.200404121814-0.snap.ximian.7.1.i586.rpm
unable to register rpm file
Everything already installed

I googled around and could find nothing pertinent.  I also thought that mayhap the RPM was corrupted, but the 
size matches that listed on the ftp mirror.  Can anyone help as to why I'm getting this error?