I'm not very familiar with MIDI errors, but I found this post. It has one possible solution for overflow MIDI glitches: import the file into Audacity and export it again as a MIDI. Can you try this to see if it works?
If that doesn't work, then I'm not sure how to fix it ^^; if you can provide a link to the MIDI you're using, someone else may be able to figure it out.
When you import a midi into UTAU it's common for the tempo to go out of wack.
Go all the way to the start of the UST until you can't go back anymore.
At measure 0 you'll see a tempo marker.
Right click on it and 'remove tempo marker'.
Then go to your normal tempo box up top and click on it. Enter the proper tempo for the song.