OK, let's clarify things a bit more,
I have a server certificate (wifielche_umh_es.crt) issued by a CA in response to CSR from my 6000 controller,
The complete certificate chain is:
AddTrustExternalCARoot ->UTNAddTrustServer_CA->TERENASSLCA->wifielche_umh_es, so what I'm trying to do is open my certificate wifielche_umh_es.crt and append at the begining the sequence UTNAddTrustServer_CA->TERENASSLCA->wifielche_umh_es (see wifi_elche jpg). (Three BEGIN-END sequences)
Then, I try to import the certificate into the controller and I get the error.