My Bitcoin wallet doesn't synchronize My wallet is two weeks behind in synchronizing with the net. It sais I have 8 connections with the net, however...
On top of my walletscreen it says: "Warning: Shown transactions are possible incorrect! You might need to upgrade, or other nodes need to upgrade."

How to solve this problem?
You may need to upgrade is an indicator that you may be running a client that is no longer viable for use on the network.  Download the current version 0.8.6 at this time.  There was at least one hard fork in the network that caused older versions to be deprecated.