What is APR?

I own a parcel on the border of a mainland sim. Often when I invited guests over, they would complain of the lag, saying it was unbearable. I never had any problem with lag, so I assumed it was just their machine or connection and went on my merry way.

After a few more complaints, I installed a few lag monitors to track fps and dilation so that I could help gauge what exactly was going on. FPS usually stays about 44, and the dilation rarely reaches below 75%. Still, I had no problem with lag, so I went on with my assumption that it was client-side lag for others.

Then one day I created an alt. Now I've noticed that when I swap from the alternate character to my main character (or vice-versa) that the lag is horrendous! I sit sometimes 5 minutes to let sculpties and textures load. Movement is stilted, and scripts respond very very slowly. FPS and dilation appear to be roughly the same as when I'm not experiencing this lag.

Well, to better understand this, I opened up the client menu and went looking around at the consoles.

When I look at the debug console, I get the same message over and over: "WARNING: 11_apr_warn_status: APR: Invalid argument
WARNING: 11_apr_warn_status: APR: No connection could be made because the target machine actively refused it."

1) What is "APR?"

2) Does it have anything to do with the lag I'm experiencing? Or should I look somewhere else for the culprit?

3) How can I help correct the situation?

I realise APR may be totally unrelated to the lag, but it'd be handy to know what it is.