The selected OVF is referencing more files than you are uploading: <filename>.vmdk, .VMware Cloud Director 10.6.1
Currently VCD does not handle the EnvironmentFilesSection from the ovf. VCD validates OVF descriptors against the OVF 1.0 specification.
VCD is validating with https://schemas.dmtf.org/ovf/envelope/1/ and 1.x xsd versions doesn't support EnvironmentFilesSection.
Additional Info EnvironmentFilesSection is in xsd version 2.0. Refer https://schemas.dmtf.org/ovf/envelope/2/dsp8023.xsd
Since, VCD does not handle the EnvironmentFilesSection from the ovf, it is currently unsupported and the following workarounds are available:
EnvironmentFilesSection from the OVF descriptor file after extracting the OVA.