Error Importing SSL certificate : Not an X.509 Certificate

Many CAs will provide a cert in PKCS7 format.

According to Oracle documentation, the keytool commmand can handle PKCS#7 but sometimes it fails

The keytool command can import X.509 v1, v2, and v3 certificates, and PKCS#7 formatted certificate chains consisting of certificates of that type. The data to be imported must be provided either in binary encoding format or in printable encoding format (also known as Base64 encoding) as defined by the Internet RFC 1421 standard. In the latter case, the encoding must be bounded at the beginning by a string that starts with -----BEGIN, and bounded at the end by a string that starts with -----END.

If the PKCS7 file can't be imported try to transform it from PKCS7 to X.509:

openssl pkcs7 -print_certs -in certificate.p7b -out certificate.cer

Does your cacerts.pem file hold a single certificate? Since it is a PEM, have a look at it (with a text editor), it should start with

-----BEGIN CERTIFICATE-----

and end with

-----END CERTIFICATE-----

Finally, to check it is not corrupted, get hold of openssl and print its details using

openssl x509 -in cacerts.pem -text

This seems like an old thread, but I'll add my experience here. I tried to install a cert as well and got that error. I then opened the cer file with a txt editor, and noticed that there is an extra space (character) at the end of each line. Removing those lines allowed me to import the cert.

Hope this is worth something to someone else.