RTMPT stops working. Error: Failed to signal process condition: errno(43)

Using licensed FMIS v4.5.1 r484 x64.

RTMPT stops working every once in a few days. Restarting FMS fixes the issue. When the problem occurs both RTMP and RTMPT connections generate the following error in master.00.log:

Failed to signal process condition: errno(43)

Despite the error RTMP works but RTMPT does not. There seems to be quite a bit of memory released after restarting FMS:

Before restart:

             total       used       free     shared    buffers     cached

Mem:      16426572   13315052    3111520          0     267948    9108452

-/+ buffers/cache:    3938652   12487920

Swap:     10217332          0   10217332

After restart:

             total       used       free     shared    buffers     cached

Mem:      16426572    6244816   10181756          0     301292    3124848

-/+ buffers/cache:    2818676   13607896

Swap:     10217332          0   10217332

What does this error mean? Is FMS running out of memory? The server has 16 GB of RAM. There are about 270 vhosts it loads but on average only about 60-100 connections at any time.