Estou tentando se conectar a um serviço seguro através de um proxy usando o comando curl, mas recebo o seguinte erro:

Não é possível carregar o certificado de cliente -8018.

Log completo:

[e-ballo@myserver]#   curl  -v -x proxy01.net:8080 https://endPointURL.com/SOAP --key ./cert.crt --cert ./cert.crt -capath=/etc/pki/tls/certs
* About to connect() to proxy proxy01.net port 8080 (#0)
*   Trying 10.0.3.64... connected
* Connected to proxy01.net (10.0.3.64) port 8080 (#0)
* Establish HTTP proxy tunnel to endPointURL.com:443
> CONNECT endPointURL.com:443 HTTP/1.1
> Host: endPointURL.com:443
> User-Agent: curl/7.19.7 (x86_64-redhat-linux-gnu) libcurl/7.19.7 NSS/3.14.3.0 zlib/1.2.3 libidn/1.18 libssh2/1.4.2
> Proxy-Connection: Keep-Alive
>
< HTTP/1.0 200 Connection established
<
* Proxy replied OK to CONNECT request
* Initializing NSS with certpath: sql:/home/e-ballo/
* Unable to initialize NSS database
* Initializing NSS with certpath: none
*   CAfile: /etc/pki/tls/certs/ca-bundle.crt
  CApath: none
* Unable to load client cert -8018.
* NSS error -8018
* Closing connection #0
curl: (58) Unable to load client cert -8018.

Alguma ideia do que este erro significa? e como posso consertar isso?

Desde já, obrigado,