Java SE (Java Platform, Standard Edition)

Dear java experts,

I am trying to hack some of my own code into a file upload applet I got off Sourceforge. I know two things so far... my code works when it's in my separate test applet and the ZUpload applet works before I modify it.

I have put my code into ZUpload and it compiles ok. I have packed it all up into a new jar and signed it.

The new jar contains:
/MyModifiedZUpload.class
/MyNewAdditional.class
/ [the various packages needed by ZUpload]

When I try and use the new jar I get the dreaded:
java.security.AccessControlException: access denied (java.util.PropertyPermission user.dir read)

I have been searching for info about this error but it seems it's usually due to unsigned applets... but I've signed mine into a new jar so it can't be that...? If anyone can point me in the right direction it's much appreciated. Yes, I am a humble newbie.

cheers!