There are a number of common issues that would cause the CSR to be invalid. When you created the CSR you will have been asked for several pieces of information :
Check the common name field.
You may have specified an IP address (e.g. 178.0.1.23) or a server name (e.g. mywebserver) instead of a Fully Qualified Domain Name such as www.mydomain.com or domain name such as mydomain.com. You must specify a Fully Qualified Domain Name or domain name to enroll for a RapidSSL or GeoTrust Certificates.
Make sure you do not have any illegal characters in any of the fields in the CSR. Illegal characters are [! @ # $ % ^ ( ) ~ ? > < & / \ , . " ']
Check the country field.
If you are located in the United Kingdom, do not specify your country code when generating the CSR as "UK" - it must be "GB".
Make sure you have included the header and footer of the CSR into the enrollment form. The header and footer will look like:
----BEGIN CERTIFICATE REQUEST -----
encoded data
-----END CERTIFICATE REQUEST------
Make sure that there are 5 dashes on each side of Begin and End certificate request. There should also be no trailing spaces in the CSR. You will need to ensure you have select the CSR key size is 2048 bits.
