Hello Simon,
The issue that you are seeing is due to the fact that serial communications methods in LabVIEW were changed between LabVIEW 6.1 and LabVIEW 7.x. The serial compatibility vi's that you were using were modified to make use of VISA, and users were advised to just use the lower level VISA functions instead.
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It is possible to use the old version of the serial within LabVIEW 7.x but this is not supported. You will need to copy some of the files from the older version of LabVIEW in order to make this work. This will affect these vi's for every application that you create. For newer applications it is advised that you use VISA instead. Before you do this, make sure that you open your vi, and that it is using the vi's from the LabVIEW 7.1 installation - and not any vi's that you may have bundled with it into a llb.
1. Replace the serial.llb in LabVIEW 7.x with the serial.llb from a previous version of LabVIEW. This file is found in C:\Program Files\National Instruments\LabVIEW\vi.lib\instr.2. Replace the _sersup.llb file in LabVIEW 7.x with the _sersup.llb from a previous version of LabVIEW. In LabVIEW 6i and 6.1 this file is located in C:\Program Files\National Instruments\LabVIEW\vi.lib\platform. In LabVIEW 7.x (and 5.x) this file is found in C:\Program Files\National Instruments\LabVIEW\vi.lib\instr. 3. Copy the file serpdrv to the C:\Program Files\National Instruments\LabVIEW 7.x directory. This file is not installed with LabVIEW 7.x, so it only needs to be copied from a previous version of LabVIEW, not replaced.
This should work, and then your application will run using the older version of the vis. But like I said this is not supported, and it is recommended that you upgrade the application to make use of the VISA functions instead.
I hope this helps, let me know if you have any issues
RegardsHannahNIUK & Ireland