Conversion of JXR to jpg

[cvh]

Win10 x64
I am using MS Image Composite Editor to creat panoramas. Occassionally it spits out a file in jxr format. I want to convert this to jpg to combine it with the jpgs normally generated.
MP claims to do the conversion but produces a file size of 0, having started with 24MB.

Is MP is the correct tool, or is this a bug?

[xnview]

yes JXR file are supported, is it possible to send a file?

[cvh]

Maybe, but it is 24 MB.
I have just tried to drag the file into the message box, but got an error "Invalid file extension: line08_09.jxr."
When I tried the add files tool, the file extension had been converted to .jpg, but then failed because "File too large: line08_09.jpg"