Quartus 7.1 Sp1 and DSPBuilder 7.1Sp1

Java is provided along with MATLAB, so it doesn't matter whether you have it installed separately on your system. If the problem was that Java wasn't there, the Signal Compiler window would not appear. You're definitely getting the following error? :

Java exception occurred:

java.lang.UnsatisfiedLinkError: checkOut

at com.altera.dspbuilder.portmanager.PortManager.checkOut(Native Method)

at com.altera.dspbuilder.serialisation.ModelSerialiser.<init>(ModelSerialiser.java:88)

I also think the mpr.dll problem is a red herring since without it, I think your computer would have other problems - it seems to be quite important to Windows. Only other thing I can suggest is to check your MATLAB console window to see if there are any earlier error messages.