Maybe this is related to the certificate issue identified below. If the cert use to sign the code of the extension is not recognized on the ePO server, then the extension check in will fail.
VSE 8.8 Patch 7
Issue: VSE 8.8 Patch 7 installation fails because of a certificate chain failure. Issue discovered: March 18, 2016
Workaround: For available workarounds, see the related articles.
Thanks Andre, problem solved