VNAV bug after reformat of HD

Hi.I've just reformated my harddisk, and installed everything all over.I installed the PMDG base pack, restarted the PC, installed SU1.1, restarted and cranked up. Started the aircraft and programmed the FMC like normal.Now, when in VNAV mode, when I get close to the step altitude set by ATC, the aircraft suddenly start to skyrocket to the ground. I have to disengage the AP and level of manually to recover.VNAV works ok when I approach the final cruise altitude (it levels of smoothly), so it only happens when approaching step altitudes.I used the removal tool to uninstall, and installed again, but same problem. I checked the correct options for FS9 when I installed both. Using the same files to install.Using FS9 and Win XP Pro (SP1) on a P4 2,53GHz running at 2.8GHz, 1GB DDR-RAM, GF4 Ti4800SE 128MB. I have registered versions of FSUIPC and Active Camera 2004, and I'm running MyTraffic 2004.I never had this problem before the reformat.Any suggestions are most welcome. Please help before I go nuts... *:-*Regards,Bj