cannot yield (take 2)

cannot yield: C stack busy
    while executing
"::yield"
    (class "::Coroonet" method "_yield" line 3)
    invoked from within
"my _yield $socket INCOMING"
    (class "::Coroonet" method "get" line 4)
    invoked from within
"my get $socket"
    (class "::SMTP" method "response" line 4)
    invoked from within
"my response $socket"
    (class "::SMTP" method "senddata" line 14)
    invoked from within
"my senddata $socket 3000 $msg"
    ("3*" arm line 2)
    invoked from within
"switch -glob $code {
			    3* {
				lassign [my senddata $socket 3000 $msg] code response
				puts stderr "sent data: $code"
				dict set status data..."
    (body of "dict with")
    invoked from within
"dict with smtp {
	    lassign [my send $socket 60000 EHLO $client] code response
	    dict set status EHLO [list $code $response]

	    switch -glob -..."
    (class "::SMTP" method "smtp_server" line 23)
    invoked from within
"my smtp_server $socket $msg $smtp"
    (class "::SMTP" method "smtp" line 14)
    invoked from within
"my smtp ::mime::1 {client thighbone syncvar ::status completion {} servers {puretcl.com localhost} multiple 0 atleastone 1 queue 1 xverp 1 mode MAIL m..."
    invoked from within
"::oo::Obj5::C1 INCOMING"