Clone HDD in RAID1

I do not understand:
" However, both HDDs contain the same data files. "

It sounds to me like you had a raid configuration, which is broken now. So your system boots a raid1 where only one member is available. After the boot is finished the second hard disk is recognised.

In short this means even though the files on both disk look similar, only one of them contains a working raid configuration - meaning only on can be cloned.

In addition you have to be careful with IDE drives switching from slave to master or the other way around can also break your boot record. Just in case!
If you plugged in the disks in another system and tried to copy them there, that might already destroyed your working configuration.

On the other hand if the system is at least booting, you can try to start Acornis from an bootable disk, they seem to be more successful when it comes to copying windows xp pro raids, like explained on their site: http://www.acronis.com/en-us/company/inpress/2007/03-15-boot-loader-2.html

What is the reason you want to clone it?
If the OS is bootable go to Windows Disk Management (right click on My Computer - Manage - Disk Management) - how many drives you see? If 1 then it is hardware RAID.
If you put the HDD or OS from RAID to a single drive in non-RAID mode then it will fail to start. Because the OS should be adjusted to new hardware. See here how: https://www.experts-exchange.com/articles/2569/Windows-OS-migration-to-dissimilar-new-hardware-How-to-move-your-system-to-new-hardware-without-OS-reinstallation.html

>>  and when I tried to install it on a separate PC and start it then I got an errior msg : Error Loading operating system   <<  if this system has different (modern) hardware - that can be normal

for different hardware, you need the paragon Adaptive restore :  http://www.paragon-software.com/technologies/components/adaptiverestore/

the 2 new HDs that I purchase are SSD and the ones I want to clone are IDE, then this will broke the RAID config and for this reason I was not able to clone them

Now, I got 2 new IDE HDs and it is working fine

thanks all for your assistance

Thanks

Ok, the motherboard which was designed to work with IDE drives would apparently have problems with SSD drives.

what's more - you did not post the size and model of the old drives notr the  SSD's
by leaving out many info- it's impossible for us to help you correct
also note that SSD's need TRIM in XP

You are also violating your licensing agreement.  It's against the EULA to clone a drive and run it on another without purchasing another license.

What you really need to do is put both drives back in the original system. Make an Image backup of it with Acronis but when you go to restore the image use Universal Restore. This will allow you to restore it to dis-similar hardware and have it boot.