Update vhd-not-supported-vm-azure.md

Author: genlin

support/azure/virtual-machines/windows/vhd-not-supported-vm-azure.md

@@ -34,12 +34,13 @@ ErrorMessage: The specified cookie value in VHD footer indicates that disk 'disk
 This problem occurs for one of the following reasons:
 
 - The VHD does not comply with the 1 MB alignment (offset). The supported disk size should be 1 MB * N. For example, the disk should be 102,401 MB.
+- The disk has unallocated spaces. The unallocated spaces are valid in a dynamic disk and may not contain metadata or data, but their presence can complicate the conversion to a fixed disk and cause errors.
 - The VHD is corrupted or not supported.
 
 ## Resolution
 
 > [!NOTE]
-> To perform the following fix, the customer will need to perform these steps prior to uploading the VHD into Azure.
+> To perform the following fix, you will need to perform these steps prior to uploading the VHD into Azure.
 
 To resolve this problem, resize the disk to comply with 1 MB alignment: