For XitNotes versions up to vesion 1.0i You must have Lotus Notes 5 and above. It is most likely you are running Lotus Notes version 4.6.
Also there are 2 versions. One for Version 5.0 - 5.05 and one for version 5.05 and above (including version 6) version. The 5.06 version (XitNotes 1.0i) is mainly needed for Notes 6 but fixes a few bugs in the notes libraries (LCPPN22.DLL which is replaced with LCPPN23.DLL) that may help avoid any possible issues in Lotus Notes 5.06 and above.