MacOS X - Unable to perform update

I'm unable to perform updates on my MacBook, version 10.5.6.

When I search for updates for my Mac, I'm getting the following message:

• "Updating software can not locate the server update. Check your Internet connection and try again. Update software can't search for new updates because of a network problem."
• I ran a network diagnostic , but everything seemed OK.

Solution

Your problem may be due to the presence of an antispyware software (LittleSnitch or NetBarrier ), or perhaps you accidentally blocked access to the server update Apple.

• Open "System Preferences / Software Update" and check or uncheck 'Automatically check for updates "and select the frequency of searches (daily, weekly, monthly)
• Disable your antispyware program momentarily (during update search)

Note that

For an updated Mac OS X, I recommend to always use the Combo update and not the automatic update tool proposed by the 'Software Update'. The advantage is to get at once all the interim updates (Security Update,...). The disadvantage is that it is cumbersome to download.

• Go to 'Applications / Utilities / Disk Utility disk' and run a repair permissions
• Download and run the Combo Update 10.5.6
• Start again > repair permissions
• Run the update utility software to retrieve the latest updates.

Thanks to Ritchi