Error problem

Hello hello,
This is the message that appears when loading the ontology.
Please help me cause I don't want to lose my work.
My e-mail is: gdiako@aegean.gr
Please reply my as soon as possible.

Regards
M. Diakogianni



There were errors at performing operation.

1. An error occurred at parsing the OWL ontology 

    file:/C:/Documents%20and%20Settings/Vaio%20User/Επιφάνεια%20εργασίας/Tutorial%20Protege%20Example/Pizza%20Example/Pizza.owl

    at line -1 and column -1.
    Jena parse error message: Premature end of file.
    Exception class org.xml.sax.SAXParseException.  Message: Premature end of file.

2. Exception class java.lang.NullPointerException

3. Errors at loading OWL file from file:/C:/Documents%20and%20Settings/Vaio%20User/Επιφάνεια%20εργασίας/Tutorial%20Protege%20Example/Pizza%20Example/Pizza.owl

Please consider running the file through an RDF or OWL validation service such as:
  - RDF Validator: http://www.w3.org/RDF/Validator
  - OWL Validator: http://phoebus.cs.man.ac.uk:9999/OWL/Validator


4. An error occurred at parsing the OWL ontology 

    file:/C:/Documents%20and%20Settings/Vaio%20User/Επιφάνεια%20εργασίας/Tutorial%20Protege%20Example/Pizza%20Example/Pizza.owl

    at line -1 and column -1.
    Jena parse error message: Premature end of file.
    Exception class org.xml.sax.SAXParseException.  Message: Premature end of file.

See console and log for more details.