it shows startup disk is full but i use just only 350gb of my hd disk from 500gb.

If you select your HDD's Desktop icon, then Press COMMAND-I to open the Get Info window, what is shown in the upper panel for capacity, used, and available?

That pretty clearly shows the drive is full. So first a question: Why do you believe there's an error? How do you know there's only 350 GB in use? Second is to do the following:

Repair the Hard Drive and Permissions - Lion

Boot to the Recovery HD:

Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.

Repair

When the recovery menu appears select Disk Utility. After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list. In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive. If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported then click on the Repair Permissions button. When the process is completed, then quit DU and return to the main menu. Select Restart from the Apple menu.

Again, check your drive usage for any changes.

OmniDiskSweeper (free) - http://www.omnigroup.com/applications/omnidisksweeper/download/

OS X Lion: About Time Machine's "local snapshots" on portable Macs - http://support.apple.com/kb/HT4878 - “You may notice a difference in available space statistics between Disk Utility, Finder, and Get Info inspectors. This is expected and can be safely ignored. The Finder displays the available space on the disk without accounting for the local snapshots, because local snapshots will surrender their disk space if needed."

Hidden local backups with Mac OS X Lion filling up your MacBook hard disk! - http://blog.valerio.de/post/19238158977/hidden-local-backups-with-mac-os-x-lion- filling-up-your - Time Machine using local drive to store backups when external drive is not available.

I have exactly the same problem and i ve tryed everything!

steixeira - As a courtesy to the original poster (OP) I suggest starting a new topic with your question. Discussions primarily focus on just a single person's question unless yours is truly identical in which case you don't have to ask it. For all we know, our suggestions have solved the original poster's question, but clearly not yours so it isn't the same problem. Go to the next level up in the forum and start a new topic.