All 32bit-only applications crash instantly

After upgrading to Lion all non-64bit applications crash right after starting. Universal binaries that contain x86_64 code just wor fine.

e.g. Dropbox crashes, ExpanDrive works

$ file /Applications/Dropbox.app/Contents/MacOS/Dropbox

/Applications/Dropbox.app/Contents/MacOS/Dropbox: Mach-O universal binary with 2 architectures

/Applications/Dropbox.app/Contents/MacOS/Dropbox (for architecture ppc): Mach-O executable ppc

/Applications/Dropbox.app/Contents/MacOS/Dropbox (for architecture i386): Mach-O executable i386

$ file /Applications/ExpanDrive.app/Contents/MacOS/ExpanDrive

/Applications/ExpanDrive.app/Contents/MacOS/ExpanDrive: Mach-O universal binary with 2 architectures

/Applications/ExpanDrive.app/Contents/MacOS/ExpanDrive (for architecture i386): Mach-O executable i386

/Applications/ExpanDrive.app/Contents/MacOS/ExpanDrive (for architecture x86_64): Mach-O 64-bit executable x86_64

Any pointer are highly appreciated.

TIA,

Andreas