[BSPeter]

From where did you download and how did you install BSPlayer?
Did you use an exe installation, or just unpacked a zipped version?
The file bsrendv.dll is part of BSPlayer upto and incl. build 501 of version 0.86. In this version it forms a (matched) pair with bplay.exe and should be in the installation folder of BSPlayer. (Note: bplay.exe and bsrendv.dll originating from different builds usually do not work together!)
(In the newest version RC1.0 build 805 this pair is formed by bsplay.exe and bsrendv2.dll)

You can download version 1.0 build(s) as well as version .86 build 501 here (501 available as zip and/or as exe=install file), here (501=zip-file) or here (501=exe-file) [version 1.0 build(s) = exe-file on all three sites; the last site however hasn't got the latest build of version RC1.0 at present]
If you wish to be sure that you've got the latest version, you better download it from the site of its creator bst, i.e. here.)