I think I have found the solution, indirectly you pointed me in the direction to follow and for that I am grateful as the solution would not have become apparent otherwise.
I got a friend to format the drive on his PC. When he opened the drive his PC would only see the drive as one containing 200MB and with one partition. A little small considering it is 128Gb. No way at all could Windows see this drive as a 128GB one. However, we formatted the 200MB that could be seen.
Back home I then accessed the drive using DiscUtility and now it said the drive had two partitions, one was 200Mb and the other the remainder. I should say that at no time along the whole process was it formatted other than with one partition and DiscUtility has always until now only reported it seeing one partition. Windows though saw something else, a second partition that nobody knew existed but it could not see the main one.
On the 200MB I now had I found that in the app the drive was seen, I could add a folder called “Photos” and put a file in it. All working. But in a 200MB partition.
Therefore it had to be something to do with the formatting on the MAC. I reformatted the drive as exFAT and got back to one partition of 128Gb. However, the MAS OS in DiscUtiity formatting defaults to GUID Partition as the Scheme. I changed this to “Master Boot Record” and formatted again. Added files and this time the app now sees them.
Two things therefore, there is perhaps a second partition that does not appear normally on the drive but Windows could see it and the app wants to use it. Or formatting on the MAC and selecting one partition still for some reason creates two, a small one and a big one but on the MAC you cannot see the small one but the app can. Mysteriously even if one partition is chosen for formatting in MAC OS there are still two on the drive.
The solution for anybody else with the problem seems therefore that if formatting on a MAC, choose exFAT and also change the default scheme to Master Boot Record.
I guess somebody with the technical knowledge can explain all this but perhaps reference can made to it in the manual for future users.
Again thanks for your help, I would not have achieved this but for your suggestion and would otherwise been sending the drive back to Apple!
Richard.
