The keychain that needs to be updated or deleted is the login keychain. This problem usually occurs when you reset your user login password with the Password Reset utility from a Mac OS X Install disc or the Recovery partition. Resetting the password in this way resets it for your user account, but the keychain will still be using your old (forgotten) password. The problem might also occur in some situations when changing a network login password in a network domain environment. You can try deleting the login keychain using the Keychain utility. See the following Apple support article for instructions: http://support.apple.com/kb/HT1631. Choose the option to "Delete Files & References" if that comes up. Note that you will lose any saved passwords in that keychain.
If that doesn't work, you may have to manually remove the keychain files. To do so, go to the Finder, hold down the Option key, click on the Go menu in the Menu bar, and choose Library (if you don't press the Option key, the Library folder is hidden in this menu in OS 10.8 and 10.9). Once your user Library folder is open, locate the Keychains folder and delete the file, "login.keychain." Reboot the Mac and then open Safari, Skype, or whatever program is squawking about the keychain mismatch. Follow the prompts to reset the keychain to the defaults for that application. You will need to know your current Mac login password and enter it to complete the process.
Note: I am assuming you're running OS 10.8.x since you posted in this forum--instructions may differ slightly in older systems.
Reply back if you need further help or note whether your issue is resolved.