They must be pasted this in order, the Comodo intermediate certificate first, followed by the GTE root certificate, the result will look similar to the example below (Please note: no blank line between then end of one certificate and the start of the next):
-----BEGIN CERTIFICATE-----
MIIEyDCCBDGgAwIBAgIEAgACmzANBgkqhkiG9w0BAQUFADBFMQswCQYDVQQGEwJV
UzEYMBYGA1UEChMPR1RFIENvcnBvcmF0aW9uMRwwGgYDVQQDExNHVEUgQ3liZXJU
.....
zs1x+3QCB9xfFScIUwd21LkG6cJ3UB7KybDCRoGAAK1EqlzWINlVMr5WlvHqvaDj
vA2AOurM+5pX7XilNj1W6tHndMo0w8+xUengDA==
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
MIIB+jCCAWMCAgGjMA0GCSqGSIb3DQEBBAUAMEUxCzAJBgNVBAYTAlVTMRgwFgYD
VQQKEw9HVEUgQ29ycG9yYXRpb24xHDAaBgNVBAMTE0dURSBDeWJlclRydXN0IFJv
.....
IjeaY8JIILTbcuPI9tl8vrGvU9oUtCG41tWW4/5ODFlitppK+ULdjG+BqXH/9Apy
bW1EDp3zdHSo1TRJ6V6e6bR64eVaH4QwnNOfpSXY
-----END CERTIFICATE-----
NOTE: Restarting Apache will NOT work. You must stop the service, then start it again to complete the installation