You have to specify a valid country code in Certificate Signing Request (CSR).
Although usually country codes for CSRs match Internet top-level domains (TLD), it's not always the case. For example, CSR with country code "UK" will be invalid for United Kingdom (although confusingly, country TLD domain is .uk); you must provide "GB", as in Great Britain - otherwise, you will get "CSR country code invalid", "Country Code Is Not Valid", "You submitted a CSR that contains an invalid country code" or similar error from your SSL vendor.
Below, a full list of valid country codes for SSL certificates (2 lettered ISO-3166 country codes):
Country codes
AX Åland Islands
AD Andorra
AE United Arab Emirates
AF Afghanistan
AG Antigua and Barbuda
AI Anguilla
AL Albania
AM Armenia
AN Netherlands Antilles
AO Angola
AQ Antarctica
AR Argentina
AS American Samoa
AT Austria
AU Australia
AW Aruba
AZ Azerbaijan
BA Bosnia and Herzegovina
BB Barbados
BD Bangladesh
BE Belgium
BF Burkina Faso
BG Bulgaria
BH Bahrain
BI Burundi
BJ Benin
BM Bermuda
BN Brunei Darussalam
BO Bolivia
BR Brazil
BS Bahamas
BT Bhutan
BV Bouvet Island
BW Botswana
BZ Belize
CA Canada
CC Cocos (Keeling) Islands
CF Central African Republic
CH Switzerland
CI Cote D'Ivoire (Ivory Coast)
CK Cook Islands
CL Chile
CM Cameroon
CN China
CO Colombia
CR Costa Rica
CS Czechoslovakia (former)
CV Cape Verde
CX Christmas Island
CY Cyprus
CZ Czech Republic
DE Germany
DJ Djibouti
DK Denmark
DM Dominica
DO Dominican Republic
DZ Algeria
EC Ecuador
EE Estonia
EG Egypt
EH Western Sahara
ER Eritrea
ES Spain
ET Ethiopia
FI Finland
FJ Fiji
FK Falkland Islands (Malvinas)
FM Micronesia
FO Faroe Islands
FR France
FX France, Metropolitan
GA Gabon
GB Great Britain (UK)
GD Grenada
GE Georgia
GF French Guiana
GG Guernsey
GH Ghana
GI Gibraltar
GL Greenland
GM Gambia
GN Guinea
GP Guadeloupe
GQ Equatorial Guinea
GR Greece
GS S. Georgia and S. Sandwich Isls.
GT Guatemala
GU Guam
GW Guinea-Bissau
GY Guyana
HK Hong Kong
HM Heard and McDonald Islands
HN Honduras
HR Croatia (Hrvatska)
HT Haiti
HU Hungary
ID Indonesia
IE Ireland
IL Israel
IM Isle of Man
IN India
IO British Indian Ocean Territory
IS Iceland
IT Italy
JE Jersey
JM Jamaica
JO Jordan
JP Japan
KE Kenya
KG Kyrgyzstan
KH Cambodia
KI Kiribati
KM Comoros
KN Saint Kitts and Nevis
KR Korea (South)
KW Kuwait
KY Cayman Islands
KZ Kazakhstan
LA Laos
LC Saint Lucia
LI Liechtenstein
LK Sri Lanka
LS Lesotho
LT Lithuania
LU Luxembourg
LV Latvia
LY Libya
MA Morocco
MC Monaco
MD Moldova
ME Montenegro
MG Madagascar
MH Marshall Islands
MK Macedonia
ML Mali
MM Myanmar
MN Mongolia
MO Macau
MP Northern Mariana Islands
MQ Martinique
MR Mauritania
MS Montserrat
MT Malta
MU Mauritius
MV Maldives
MW Malawi
MX Mexico
MY Malaysia
MZ Mozambique
NA Namibia
NC New Caledonia
NE Niger
NF Norfolk Island
NG Nigeria
NI Nicaragua
NL Netherlands
NO Norway
NP Nepal
NR Nauru
NT Neutral Zone
NU Niue
NZ New Zealand (Aotearoa)
OM Oman
PA Panama
PE Peru
PF French Polynesia
PG Papua New Guinea
PH Philippines
PK Pakistan
PL Poland
PM St. Pierre and Miquelon
PN Pitcairn
PR Puerto Rico
PS Palestinian Territory
PT Portugal
PW Palau
PY Paraguay
QA Qatar
RE Reunion
RO Romania
RS Serbia
RU Russian Federation
RW Rwanda
SA Saudi Arabia
SB Solomon Islands
SC Seychelles
SE Sweden
SG Singapore
SH St. Helena
SI Slovenia
SJ Svalbard and Jan Mayen Islands
SK Slovak Republic
SL Sierra Leone
SM San Marino
SN Senegal
SR Suriname
ST Sao Tome and Principe
SU USSR (former)
SV El Salvador
SZ Swaziland
TC Turks and Caicos Islands
TD Chad
TF French Southern Territories
TG Togo
TH Thailand
TJ Tajikistan
TK Tokelau
TM Turkmenistan
TN Tunisia
TO Tonga
TP East Timor
TR Turkey
TT Trinidad and Tobago
TV Tuvalu
TW Taiwan
TZ Tanzania
UA Ukraine
UG Uganda
UM US Minor Outlying Islands
US United States
UY Uruguay
UZ Uzbekistan
VA Vatican City State (Holy See)
VC Saint Vincent and the Grenadines
VE Venezuela
VG Virgin Islands (British)
VI Virgin Islands (U.S.)
VN Viet Nam
VU Vanuatu
WF Wallis and Futuna Islands
WS Samoa
YE Yemen
YT Mayotte
ZA South Africa
ZM Zambia
Restricted country codes
The following countries are restricted by US Export restriction laws, therefore some SSL vendors won't issue certificates for registrants in the following countries:
AF Afghanistan
CI Cote D'Ivoire
CU Cuba
ER Eritrea
GN Guinea
IR Iran, Islamic Republic of
IQ Iraq
KP Korea, Democratic People's Republic of
LR Liberia
MM Myanmar
RW Rwanda
SL Sierra Leone
SS South Sudan
SD Sudan
SY Syrian Arab Republic
ZM Zimbabwe
Original top-level domains
Some SSL vendors may have the following original top-levels domains listed as accepted country codes:
COM US Commercial
EDU US Educational
GOV US Government
INT International
MIL US Military
NET Network
ORG Non-Profit Organization
ARPA Old style Arpanet
Brand top-level domains
Even if you have a brand top level domain, you'll have to specify a valid country in the CSR.