i have the following JNLP file:
TCM 201
I had the same problem when compiling on my linux maschine (with JDK 6 U45). But I got this error only when I also tried to start the signed application with Java 6 U45.
When I try to start the application with a newer Java-Version (e.g Java 8) it was OK all the time, with no error message.
When I used a windows maschine to compile the project (also with 6 Update 45), it strangely works also when I use Java 6 U45 to start.
Just my 2 cents.... Cheers!