Product Version: NetBeans IDE Dev (Build 200810100201)
Java: 1.6.0_10-rc; Java HotSpot(TM) Client VM 11.0-b15
System: Windows XP version 5.1 running on x86; Cp1250; cs_CZ (nb)

I created sample java project and initialized it as a hg repository and created a clone of this project.
In original project a made some changes and (from the project root) invoked Export Uncommitted Changes".
The patch was created, but the was no way how to apply it. I tried it on the cloned project's root without success. 
Then I reverted the changes on the original project and tried to apply it on the original project's root.
Still i obtained the same error (in the output):
unable to find 'originalrepo/Main.java' for patching

After many unsuccessful trials, I found a workaround how to apply it.
I changed the generated code in the patch file from:
Index: src/originalrepo/Main.java
--- src/originalrepo/Main.java Base (BASE)
+++ src/originalrepo/Main.java Locally Modified (Based On LOCAL)

to:
Index: src/originalrepo/Main.java
--- b/src/originalrepo/Main.java Base (BASE)
+++ b/src/originalrepo/Main.java Locally Modified (Based On LOCAL)

(added the b/ - I saw they are generated in the "Export diff" patches, so I tried it)
And it worked! The patch was applied.

Can there be a problem with the patch generating, or did I just use wrong approach?