Lotus Notes fixpack in .deb traditionally produces this error:

dpkg -i ibm_lotus_notes_fixpack-8.5.2.i586.deb
dpkg: error processing ibm_lotus_notes_fixpack-8.5.2.i586.deb (--install):
 parsing file '/var/lib/dpkg/tmp.ci/control' near line 2 package 'ibm-lotus-notes-fixpack':
 error in Version string '8.5.2-20110323.0837_FP2': invalid character in revision number

To circumvent this error, unpack the .deb archive with:
 

1. dpkg-deb --extract which extracts the files in the package.
2. dpkg-deb --control which extracts the meta-data.

Edit this metadata (/DEBIAN/controls) and remove the underscore from "_FP2". Then, rebuild the package with  dpkg --build .

Fixed!