It seems that AlphaSSL & Globalsign made a major update to their intermediate root certificates as of the 31st March 2014 (last week).
A lot of SSL resellers have not yet updated confirmation emails, and are providing outdated intermediate root certificates (last updated in 2011) which will not work.
Also in a lot of support web pages, references are made to these same old certificates.
Hopefully resellers will update their systems in coming weeks/months.
However should anyone else have problems with this, you can get the latest Root Certificates directly from the following links...
AlphaSSL : http://www.alphassl.com/support/install-root-certificate.html
Globalsign : https://support.globalsign.com/customer/portal/articles/1426602-globalsign-root-certificates