During import of XML data i got the error that the column "SUMMARY" of the table "JIRAISSUES" is too small for 259 characters (defined for 255).
This is because there are some Unicode characters in the summary which had exceeded the size of 255 bytes (but not chars)

To solve the problem i had to drop the new database and modify the oracle10 entity definition file where i had to change all VARCHAR2(xx) to VARCHAR2(xx CHAR).
Then the schema got created and i could import all data without a hassle.

More information:
http://stackoverflow.com/questions/81448/difference-between-byte-and-char-in-column-datatypes