It just happens that I have been doing the same thing. The main problem when changing from LV5.1 serial functions to LV7.1 serial functions has to do with how the original serial VI's were wired.
For example, the error code in the replacement LV7.1 serial VI's now uses the VISA error values, which are negative. If the old LV5.1 code tests for Greater-than-Zero error values, an exception isn't thrown when a VISA error is reported. The correct solution is to test for equal-to-zero, or not-equal-to-zero. (If the old code didn't do error checking the LV7.1 version won't have this problem.)
Another "opportunity" is the App Builder, do not forget to throw the "Serial Port" switch behind the "Advanced" button on the Installer tab, or the VISA serial drivers will not install.
Remember that LV7.1 implements serial in VISA, while the "traditional" serial port VI's in LV5.1 used the "old" Windows API's. I think you will like the performance of VISA serial much more.
