Believe me it is much less hassle installing mod manager, and using that. i added this on as after writing this, I remember having the same problem myself and think that was due to Dropping the folders into data folder as you can do with some mods, but if you have done this with this Mod? you have to manually copy a list of the fonts to the ini under 'Fonts' there should be instructions in the Read-Me on how to do this. I also find it works better for Oblivion than The Nexus Mod Manager which also can be obtained at the mentioned site. this also sorts Mod load orders and helps prevent CTD or 'Crash To Desktop'. If it happens you are not using a mod manager, I suggest using Oblivion Mod Manager (OBMM) which can be obtained from Tesnexus Oblivion Site. Maybe try deactivating, and then reactivating the Mod in Mod manager, and choosing Normal? There is a list of different font styles, and an option when you have chosen your font, to have large or normal! i always pick normal, and have no problems. I am not sure how you installed Darnified UI.? when using Oblivion Mod Manager, you get a list of options, which Fonts are one of.

Oblivion darnified ui too small