Getting the same error as was in this thread:
Running Windows 10 1709 and trying to create a RAID1 in Windows using Intel RST with my system drive and a blank identical drive, both are Samsung 850 EVO SSDs. Driver version is 126.96.36.1995.
The Intel RST error window that pops up reads:
(0xA00500D): An unknown error occurred while an operation was in progress. The operation could not be completed.
The Windows Event Viewer log entry is as follows:
|0: Error Missing Error String 0: failed to get file system properties: 8004256F System.Exception: 0: Error returned by IsiVolumeCreateFromDisks() in PsiData::PsiDataSource::ActionVolumeCreateFromDisks|
I noticed the bit about "failed to get file system properties" so I thought it may be a permissions issue and ran Intel RST as administrator but still the same issue.
I just recalled the part about leaving unallocated space on the system disk. So I shrank the end of the last volume on the system disk by 200MB and the RAID1 appears to be building now.
More relevant information that may help others:
The system (source) disk had two partitions. OS (C: 81GB) and GAMES (D: 384GB). I shrank the GAMES partition by 200MB. OS is the Windows 10 bootable partition.