SSE not seeing esp I place in Data directory

[agerweb]

I drop an esp in to the SSE Data directory and it no longer appears in the Load order list so that I can make it active. This must be a problem with a config file somewhere, because it used to work fine.

 

And I have another computer on which this does work OK.

 

I don't use Mod managers because I only ever have one mod, so there is not much to manage.