Unable to delete songs to connected iPhone?

Searched the forum didn't find thread that directly applied to me.

I don't auto-sync because I don't want iTunes dumping every song on my PC into my iPhone. I've been clicking on songs in iTunes and dragging them to the iPhone (same w/my iPod). Today I connected the phone while at work and noticed a couple of dupe entries in the iPhone. Tried to delete the songs and nothing happened. No error, no freeze, nothing at all. Went into Options and noticed "Manually manage music and videos" Tried to check the box (none in Options are checked so far) and got ominous message "Do you want to erase this iPhone and sync with this iTunes library?". PS It won't let me add any tunes either, although it didn't refuse when I tried this with my iPod.

Arrrgggg.... What to do?