We recently moved to a new server and I was getting this error:
Invalid Trace Directory. Additional Info:[ Unable to Write file , Trace directory not defined (Reporting Process:File Name is Null. LocalTraceSettings: {Filename: ,FileCountSuffix:1 ,TraceFileSize:10485760 ,TraceDirectory: ,TracingCallStack:Yes ,IsTracingOff:No ,LoadState:LoadSuccessfulUnreported ,RefreshTraceInt:-1 ,SiteWideRefreshTraceInt:-1 ,RegistryRefreshTraceInt:-1} ] , AppDomain:CrmAsyncService)
Turns out this is caused from CRM Tracing not being setup (and my plugin was using tracing). Go here to set it up: CRM Tracing Setup
Hope this can help point you in the right direction.