I wrote:

> FB 5.5.1 has some minor incompatibilities with OS X 10.7 Lion.
> 
> In settings
> [1] Architecture must be Intel or Universal.
> [2] In the Advanced drawer, the checkbox 'Use Compiler from Developer folder' must be ON.

I should have said that this applies if you have obtained and installed Lion (but not Xcode 4) from the App Store. Your existing Developer folder is unchanged. 

Robert P.