Java APIs

Hi,
I've got a client that, upon execution, parses and reads an XML file just before instantiating and executing a Thread (let's call it T1). This, in turn, instantiates and executes another thread (T2) that in turn does the same, instantiating and executing thread T3. This last thread should parse and read another XML file. My problem is this: while parsing and reading of the first XML file is successfully done, parsing of the second XML file results in the following error:
java.security.AccessControlException: access denied (java.util.PropertyPermission user.dir read)
looks like T3 hasn't got permission to read the user directory. What is really strange to me is that the first XML parsing is successful...
To parse XML files I've created a DOM parser that simply takes the name of the file to parse in form of string and gives back a 'Document' object, and the error comes in parsing phase.
Both XML files and java files are stored in the same directory (that makes the thing even more strange...).

Thanks in advance to anyone helping me.

Antonio