Sansa m250 2GB file adding problems

Hallo. I have a new Sansa m250 mp3 with 2GB. I am using drag and drop to transfer a bunch o'songs from my computer to the player, but it's not allowing more than, say, 600mb of songs. After that an error window pops up stating it cannot create the directory or file for "song name here". Yet when I check properties, the mp3 will show it still has like 1.6 GB of available space.

The disk that came with it apparently wants me to install WMP 9.0, but the Sansa m200 series lit states one should be able to drag and drop songs from one's computer. . .