Rendering Crashes. Please help me understand how to fix this error.

I have an MKV file I’m trying to render as an MP4 with subtitles (from SRT file). I’ve done this before recently, and sometimes it works, and sometimes it doesn’t. I have no idea why. This is the error I’m getting? Can someone explain what I’m doing wrong and how to fix it? Thanks in advance for any help.

[aac @ 0x7f2568007f80] [Eval @ 0x7f25710663c0] Undefined constant or missing ‘(’ in ‘k’ [aac @ 0x7f2568007f80] Unable to parse option value “k”
x264 [error]: high profile doesn’t support lossless [libx264 @ 0x7f2568001c80] Error setting profile high.