I am unable to write files to my OTG usb storage I bought a Sandisk 32GB Ultra OTG pen-drive yesterday and it was working fine, as in would allow me to both read/write through my Moto G(2nd Gen). 

Last night, I plugged it into my Samsung Galaxy note Gt N7000, just to check if it can read files too and it could read/write without batting an eye. Today when I tried to move a video file to the OTG storage using my Moto, it would give me an error saying "the following items have not been pasted". Basically, I am unable to write anything to my OTG using the Moto G. It works fine with the GTn7000 though. I cannot understand what might be causing the problem. 

I tried formatting the OTG to FAT32 with default allocation size and that too was unable to solve the problem.


Click to enlarge
On lollipop, the 3rd party apps need to support the Storage Access Framework to write to external sdcards or OTG drives.  

The apps need to be updated to support Storage Access Framework, the app developers need to be informed.  

And considering the question old, many apps should have got updated by now. And the screenshot posted by you explains that the file manager is com.rhmsoft.fm which I'm sure is updated to support this feature as of now.  

And through modifying the platform.xml, used to work in kitkat, but is not guarenteed on lollipop. There are reports that it doesn't work on lollipop.