Microsoft Software Installer error was encountered

During an install using setup on Vista (build 5308) I get the following
error: "Error 1904. Module mymodule.dll failed to register.
HRESULT -2147467229. Contact your support personnel." Looking up the error
code I get: "A Microsoft Software Installer error was encountered." Now the
strange part. If this error is on the screen (Setup still running), I cannot
even register mymodule manually (running regsvr32.exe). However, as soon as
Setup finishes, I can run "regsvr32 mymodule.dll" and the module registers
OK. Looking at the .msi, mymodule.dll is self registered.



Any ideas?