Error No: 1075, 1068, 1075, 1091 while upgrading to 2.x

I have tried to update from OC 1.5.6.4 to 2.0.3.1 and getting the following errors. Kindly help

Notice: Error: Incorrect table definition; there can be only one auto column and it must be defined as a key
Error No: 1075
Error in: /home/xxxx/public_html/install/model/upgrade.php line 249
ALTER TABLE `ocart_api` DROP PRIMARY KEY in /home/xxxx/public_html/system/library/db/mysql.php on line 55

Notice: Error: Multiple primary key defined
Error No: 1068
Error in: /home/xxxx/public_html/install/model/upgrade.php line 260
ALTER TABLE `ocart_api` ADD PRIMARY KEY(`api_id`) in /home/xxxx/public_html/system/library/db/mysql.php on line 55

Notice: Error: Incorrect table definition; there can be only one auto column and it must be defined as a key
Error No: 1075
Error in: /home/xxxx/public_html/install/model/upgrade.php line 301
ALTER TABLE `ocart_api` CHANGE `api_id` `api_id` INT(11) NOT NULL AUTO_INCREMENT in /home/xxxx/public_html/system/library/db/mysql.php on line 55

Notice: Error: Can't DROP 'option_value'; check that column/key exists
Error No: 1091
Error in: /home/xxxx/public_html/install/model/upgrade.php line 349
ALTER TABLE `ocart_product_option` DROP `option_value` in /home/xxxx/public_html/system/library/db/mysql.php on line 55

Warning: Cannot modify header information - headers already sent by (output started at /home/xxxx/public_html/system/library/db/mysql.php:55) in /home/xxxxt/public_html/system/library/response.php on line 12