You are likely to have one or more third party system modifications incompatible with Lion. Apple cannot possibly determine every one that must be quarantined when upgrading from Snow Leopard, so you will have to find out on your own what they may be.
Consider running EtreCheck in accordance with the following. EtreCheck does not do anything to fix the problem; it simply collects system information that may help determine what programs may be the cause:
Apple Support Communities contributor etresoft wrote a very useful app to quickly gather certain system information that may help point to a cause of this problem. Go to his website, download and run EtreCheck:
http://www.etresoft.com/etrecheck
Etrecheck will be in your Downloads folder. Open it from there. You may see the following dialog box:
Click Open - etresoft contributes to this forum frequently and can be considered a trustworthy developer.
It will take a moment to run as it collects its data.
Copy and paste its output in a reply.
Do not be concerned about anything that says "Problem" or "failed".
EtreCheck was designed to remove any personal information (such as your computer's name and serial numbers) but if you see anything that looks like an email address or any other personal information that should not be divulged to others, please delete or obscure that information when you post the reply.
When you are finished with EtreCheck, quit the program. It occupies very little space, and you can keep it or drag it to the Trash as you wish.