With GUIMiner did you use the solo tools? anyway....
...why are you solo mining?
nVidia GPUs are crap for mining and it will take you 10 YEARS 146 days
to solve a block solo!
GTX260 is like 40ish MH/s! (sell it on ebay and get an Ati 5770 or higher)https://en.bitcoin.it/wiki/Mining_hardware_comparison
I wouldn't solo without 5000MH/s = 30 days to solve.
Best way Ive seen to mine with low hash rate is this..
Bitcoin Wallet -> Recieve Coins -> New Address (if one not shown) -> Right click address -> Copy Address
GUIMiner -> Default ->
Server = Other
Hosts = pool.50btc.com
Username = right click and paste (your bitcoin wallet address) in here
Password = (leave this empty)
Port = 8332
Device = Select your GPU from the drop down list
Click File > Save Settings
Every night at UTC 00:00 coins will come into your bitcoin wallet if you are owed >BTC 0.01
To see how much you are owed go to...https://50btc.com/api/(your
bitcoin wallet address)
You won't make enough to cover your electricity costs with a GTX260 but you can see it works.