Why now that we have gone from 1024 to 2048 do we need to put the www in front of our portal site when we never used to.
I do agree with Jeff, there is no relation between sub-domain and level of encryption. The certificate is being issued to particular domain (www.domain.ext or domain.ext) that is depend of certificate buyer who specified the domain at the time of purchase.
There are different type of certificates are being issued by CA that can work on with www and without www version of your domain.
The bit encryption level does not impact the domain name used. Most likely the certificate was ordered with just domain.com instead of www.domain.com.
Depending on your vendor, you may be able to get a re-issue if this was done recently.
Also, some vendors will include both domain.com and www.domain.com if you order www.domain.com.