mySql Table creation Issue

[Nalini Sritharan]

I have a table called ums_grad_list with the description
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| sno | int(11) | NO | PRI | NULL | auto_increment |
| grad | varchar(10) | YES | | NULL | |
+-------+-------------+------+-----+---------+----------------+
and another table called ums_bloodgroup_list with the description
+------------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+------------+-------------+------+-----+---------+----------------+
| sno | int(11) | NO | PRI | NULL | auto_increment |
| bloodgroup | varchar(10) | YES | | NULL | |
+------------+-------------+------+-----+---------+----------------+

I am trying to create a new table called ums_user_data with reference to the above 2 tables.

create table ums_user_data(regno int(15) AUTO_INCREMENT, fname varchar(20), lname varchar(20), dob date, grad_sno int(11), bloodgroup_sno int(11), gender varchar(6), PRIMARY KEY(regno), FOREIGN KEY(grad_sno) REFERENCES ums_grad_list(sno), FOREIGN KEY(bloodgroup_sno) REFERENCES ums_bloodgroup_list(sno));

I am unable to create the table using the above query. When executing the query i'm getting the below error.

ERROR 1005 (HY000): Can't create table 'user_management_system.ums_user_data' (errno: 150)

What could be the reason for the error? I have checked the data type and size were exactly matching.

Note: The table ums_user_data was exist before and got deleted unexpectedly. Now the table does not exist.