I use Oracle SQL Developer to import data from Excel.
1°) I created a temporary table as a copy from my target table (15 columns) ;
2°) I created my Excel file with 15 columns, each one representing a column in my table ;
3°) I used the "Import data" function on my table (here is how : http://database.blogs.webucator.com/2011/02/27/importing-data-using-oracle-sql-developer/ ) ;
And so appears an error : "Task fail - rollback". And that's all.
I checked my Excel columns format, I checked data in this file, ...
And the weird part is that I already used this file with "Import Data" in SQL Developer 1 week ago. I just changed values in 1 column (and these new values have the same format and aren't too long for my table).