We are experiencing the same problem as another person described today on this site. We have a Sling SB500 purchased in November and a Channel Master DVR+ 7500 which we've had for about a year. Everything was working great until very recently. We had been able to remotely control the DVR+ using the Slingplayer app on a Samsung tablet.
However, though the DVR+ works as it always has, and we can use the Slingplayer on the tablet to watch whatever is on the DVR+ we can no longer use the virtual remote to control the DVR+. This has happened sometime after the beginning of 2016.
When I checked the software version on the Sling SB500 I found that there had been an automatic upgrade. Installed on the SB500 I found the following: UI apps version: 01.08.23, Firmware version 1.10.95, Hardware version 1.3.1.
I did the obvious of powering down and restarting the Sling SB500 as well as the DVR+ 7500. This made absolutely no difference.
It appears to me that the automatic update broke the virtual remote control feature of the Slingplayer app. Come on Sling, didn't anyone test first? How about a fast fix? Please.