lzt lacks stdout, is this the first time you get this freearc temp file ??
[External compressor:lzt]
packcmd = lzt -p1 -49 -b200 $$arcdatafile$$.tmp $$arcpackedfile$$.tmp
unpackcmd = lzt -d $$arcpackedfile$$.tmp $$arcdatafile$$.tmp
datafile = $$arcdatafile$$.tmp
packedfile = $$arcpackedfile$$.tmp
use this line instead
it will only use 1 CPU Core, same one i provided with mask v2.1