Hi Juan,
In order to run your program with LabVIEW 8.5 Runtime Engine, you need to compile it in 8.5. LabVIEW 7.0 should technically work for multi-core applications, but I'm not sure exactly what's causing your program to fail without testing. A quick search for multi-core application in 7.0 in the bug database did not turn up any results. If it is a bug, it's a better bet to try it in 8.5 and see if it works. Therefore, my recommendation would be to back up the application and try to compile the program in 8.5.
Please feel free to post in this thread if the newly compiled version still fails to work.
Thanks!
Yi Y.
Applications Engineer
National Instruments
http://www.ni.com/support