Unlike desktop browsers, if your mobile device has the capability to use SSL to make secure connections for web or email access, you may need to to install a "Root certificate" for the GeoTrust Equifax Secure Certificate Authority.
Background
openZpace sites offer optional SSL connections for both web and mail access. When a connection is made, the client device requests a certificate from the site. These certificates are issued by and signed by a certificate authority. Client devices typically are pre-installed with a wide selection of root certificates from certificate authorities that are used to verify web site certificates that have been issued by the relevant authority.
In order to save space, mobile devices with limited disk and/or memory may only pre-install a limited set of root certificates which may exclude the one you need to access a openZpace site.
Acquiring the GeoTrust Root certificate
The appropriate root certificate is that for the GeoTrust "Root 1 - Equifax Secure Certificate Authority" which can be found here: http://www.geotrust.com/resources/root_certificates/index.htm
The choice of the base64 or DER encoded versions will depend on what is accepted by your mobile device as will the procedure required to perform the installation. Please refer to the appropriate documentation for your mobile device.
Important information
As with any activity that has security implications for the operation of your device, before performing any action you must ensure that the procedure that you will follow is itself secure, has no unintended consequences and will not compromise the security of existing operations. Please refer to the appropriate documentation for your mobile device and/or seek advice from a trusted source.