Alice will not open Project! Help!

[Falco830]

I've been working for many long hours on this for my school project, and now all of a sudden it wont open! My back up files do, but my latest file is so far back that it would take at least a week to get back to where I ended up.

Heres what the error says:

Unable to load world: U:\Project Attempt 2.a2w


Alice version: 2.3
os.name: Windows 7
os.version: 6.1
os.arch: x86
java.vm.name: Java HotSpot(TM) Client VM
java.vm.version: 20.0-b11
user.dir: C:\Program Files (x86)\Alice\Required

Throwable that caused the error:
java.util.zip.ZipException: invalid CEN header (bad signature)
at java.util.zip.ZipFile.open(Native Method)
at java.util.zip.ZipFile.<init>(ZipFile.java:127)
at java.util.zip.ZipFile.<init>(ZipFile.java:144)
at edu.cmu.cs.stage3.io.ZipFileTreeLoader.open(ZipFil eTreeLoader.java:68)
at edu.cmu.cs.stage3.alice.authoringtool.AuthoringToo l.loadWorld(AuthoringTool.java:2030)
at edu.cmu.cs.stage3.alice.authoringtool.AuthoringToo l.loadWorld(AuthoringTool.java:1997)
at edu.cmu.cs.stage3.alice.authoringtool.AuthoringToo l.showStartUpDialog(AuthoringTool.java:1340)
at edu.cmu.cs.stage3.alice.authoringtool.AuthoringToo l.<init>(AuthoringTool.java:445)
at edu.cmu.cs.stage3.alice.authoringtool.JAlice.main( JAlice.java:153)

Heres my file: https://www.dropbox.com/s/ayqwvhyfi2...ttempt%202.a2w

If you can somehow miraculously fix this problem I will be super happy, thankyou for your time!