Offhand, these are the reasons I remember for a trace stop being stopped

1.the SQL server is stopped and started. If that is the case, you might need to create a procedure that creates your trace, and use the proc option to make it a start up proc, so every reboot/restart also restarts your trace.

2. You explicitly included a stop time in your sp_trace_create command

3. You defined a max file size, no rollover, and the trace file hits it's maximum size.

4. someone actually issued the exec sp_trace_setstatus @TRACEID, 0 ---stop trace, you must know the traceid to stop it

--#################################################################################################

--create the trace

exec sp_trace_create @traceid = @traceidout output,

@options = @myoptions, --i.e. set @myoptions = 2 -- TRACE_FILE_ROLLOVER = TRUE, SHUTDOWN_ON_ERROR = FALSE

@tracefile = @mypath,

@maxfilesize = @mymaxfilesize,

@stoptime = @mystoptime,

@filecount = @mymaxRolloverFiles

--#################################################################################################