Thanks for your reply!! I tried a few things I found online including the article you posted...this unfortunately did not solve my problem. Through some trial and error process I found the issue was with my build properties in the advanced section shown below.
I had to check LabVIEW8.x file layout to allow the subpanel VI to load into my main app. I didn't think to check this cuz my code was developed in version 2010. I'm guesssing some of the callers where originally created in older versions and needed the the LabVIEW8 file layout, even though all my source code is compiled in version 10. If you think I might be wrong on this assumption let me know.
P