Getting error code when creating an index via java

This is kinda wierd, i have few aplications in java tha what basicly do is drop a table, create the table (instad of using "delete from table", i do it this way for performance reasons), insert new data into the table, and then, when i try to create the table indexes i get this error: java.sql.SQLException: Could not open database table kinda like if the table where locked, or some one is using the table , but i'm sure nobody is. the best i can do so far is, close the connection , open a new connection , and then try to create the index, but not always work. Any ideas on what can i'm doing wrong? or how to fix this issue? Thanks in advance.