If you had an certificate with the same name already installed, you may need to remove the certificate before installing the new one. To view existing certificates, in IE, select Tools, Internet Options, and select the Content Tab. Click on Certificates to see the list of current certificates.
Once you encounter just about any problem, you will need to ask the certificate authority to re-issue a new certificate and invalidate the old certificate. While a major hassle, typically they will do this for free.
While the install will work under other browsers, generally it is recommended you use Internet Explorer (IE) to install your certificate and not any other browser, even though IE will generate several harmless warnings during the certificate installation.
If you install your certificate under Windows 7 or Vista, it cannot be moved to another PC. Installation under Windows XP, with some work, can be transferred to another PC.