Chainloading windows 7 installed on a local partition

[Pascal COMBES]

Hello everyone,
    I would want to submit you a problem I encountered when trying to 
install Ubuntu (on sda6) after having installed Windows 7 on a logical 
partition (sda5). Before the installation of Ubuntu, Windows 7 was on 
its logical partition (sda5) and it worked well. A detail : When 
installing Ubuntu, I put Grub on a separate boot partition (sda3).

    I tried to reconfigure Grub so that it boots either Ubuntu or 
Windows seven with :
menuentry "Windows 7" {
    insmod ntfs
    insmod chain
    set root = (hd0,5)
    chainloader +1
}
but it didn't work : Ubuntu boots without any problem but Windows don't. 
So I tested with the search function :
menuentry "Windows 7" {
    insmod ntfs
    insmod chain
    search --no-floppy --fs-uuid --set=root ${UUID_OF_MY_DISK}
    chainloader +1
}
and it again didn't work same problem. Notice I got the UUID with sudo 
blkid /dev/sda5.

The error message was :
Erreur lecture disque
which means "Error reading disk". As this is in French I guess that it 
is a message from Windows, isn't it?

    I read a little bit on the Internet and I found some posts that I 
think said it was possible but other pretend it isn't. But none of them 
were very clear. So, I don't know what to think that is why I'm asking : 
/Can grub chainload Wi//ndows when windows is installed on a logical 
partition? /If this is possible, may you give me some hints on why I 
didn't manage to set it up? Otherwise, I will change my partition table 
and reinstall everything in a different manner (by the way can you 
confirm to me that grub can be installed in a logical partition?)

    I give you my partition table :
primary /dev/sda1 (Dell stuff I cannot delete because of guarantee)
primary /dev/sda2 (Dell stuff I cannot delete because of guarantee)/
/primary /dev/sda3 (boot partition where grub  is installed)
logical /dex/sda5 (Windows 7)
logical /dev/sda6 (Ubuntu)
and some other (for data and swap) but I don't think you need them.

    I thank you in advance for you response and please you to excuse my 
bad English. Best regards,
Pascal COMBES