I have done a little more investigation - I first of all tried uploading an image file into the Joomla 4 Media Manager, which worked successfully, so it would suggest that the problem does not lie within xampp.
I then tried uploading a video file and an audio file into SPPB Media Manager and both worked perfectly OK and performed correctly, so it seems that the problem only occurs when trying to upload images - both jpg and png. Also when I choose the replace image option in the Image addon, when Media Manger opens up there is nothing there, it is completely empty. If I the try to open the folder option it closes the Media Manager and returns me to the SPPB page, but then nothing is selectable.
Finally I tried the same exercise in a different site within xampp, and the results were exactly the same.
All this would suggest that there is either a problem with the Media Manager in SPPB or there is a conflict in the way it operates in the xampp envirnment.
I am using Joomla 4.15 and SPPB 4.03