RichRaymont, When you go to the Physical Disks page, is there any difference in the information being shown for both drives? Also, verify if the controller firmware is current and up to date, I ask as this could be caused by out of date firmware. Lastly, do you have the option to Rebuild the drive in the drop downs? Let me know what you see.
I have a Dell server that has 6 disks in 3 Raid 1 arrays. One disk was replaced and came up as 'Foreign' so I followed the process to clear it and now it shows 'Ready'. I need to add it back into the Raid 1 mirror for Virtual disk 1 as but it won't allow me to. In OMSA I have selected System->Storage->Virtual Disks. For the second virtual disk (which is showing Degraded) I have selected Assign/Unassign Dedicated Hot Spare and then Execute but I get a message that reads: Storage Management only displays those disks that can be used as a hot spare. There are currently no disks that are available, large enough, or of the correct type to be used as a hot spare for this virtual disk The disks are identical with the same product ID etc. I would just pop the disk out and back in as a test but it is in a data center so I am trying to use remote tools to fix the problem.  
Virtual disk 1 Degraded