Hello, I got the same as you (4096) : 

D:\>fsutil fsinfo ntfsInfo D:
NTFS Volume Serial Number :        0x52a864f9a864dd4b
NTFS Version   :                   3.1
LFS Version    :                   2.0
Number Sectors :                   0x000000003e7be7ff
Total Clusters :                   0x0000000007cf7cff
Free Clusters  :                   0x0000000000f5785c
Total Reserved :                   0x0000000000000400
Bytes Per Sector  :                512
Bytes Per Physical Sector :        512
Bytes Per Cluster :                4096
Bytes Per FileRecord Segment    :  1024
Clusters Per FileRecord Segment :  0
Mft Valid Data Length :            0x0000000089b00000
Mft Start Lcn  :                   0x00000000000c0000
Mft2 Start Lcn :                   0x0000000000000002
Mft Zone Start :                   0x0000000006cb4d40
Mft Zone End   :                   0x0000000006cb7320
Max Device Trim Extent Count :     64
Max Device Trim Byte Count :       0x7fe00000
Max Volume Trim Extent Count :     62
Max Volume Trim Byte Count :       0x40000000
Resource Manager Identifier :     F59E5B7C-C569-11ED-B0AE-AC1F6B365CAA

Thanks a lot. EscapeHTML() fixed the issue. 

I don't know if it's same case as OP but I got "ERROR #5001: Create Directory failed: _err" as well when the method System.OBJ.ExportUDL() is called in parallel. Looks like there is a race condition. Create directory might fail is another process is already creating or has created that directory.