Which tool are you using to sign your ZXP? (Extension Builder, UCF.jar or ZXPSignCmd?)
What is the warning message you are seeing in Extension Manager?
Can you please also tell me the exact version of Extension Manager you are using? Please make sure you have updated to the latest version of Extension Manager CC via the Creative Cloud desktop app, or Adobe Application Manager.
I believe what you are seeing here is caused by an old bug which has since been fixed. Can you please check the exact version of Extension Manager you have by going to Help > About Extension Manager (Ayuda > Acerca de Extension Manager).
If you do not have Extension Manager CS6 version 6.0.8 or Extension Manager CC version 7.1.1, please download the updates from here:
Please let me know if that does not solve your problem. Alternatively, you may email me your ZXP file at firstname.lastname@example.org and I will investigate further.