Can you mine solo with a block erupter?
Yes you can, however the chances of you hitting a block are incredibly low so its not worth the time and the effort. You will loose money to electricity charges, you won't loose a lot of money but still a small amount of money to electricity charges.
You can compare it to buying lottery tickets, your chances of winning are incredibly low. When it comes to mining with a block erupter your chances of hitting a block are far far far, lower than winning a lottery.