can't read "expect_out(buffer)": no such variable

[greenpau]

When a connection to remote devices times out:

can't read "expect_out(buffer)": no such variable
    while executing
"parse_cli "$expect_out(buffer)""
    invoked from within
"expect {
        timeout {
            puts $session_log "timestamp='[exec date]' transaction_id='$transaction_id' rc=$ERROR_CONNECTION_TIMEOUT timeou..."
    ("while" body line 7)
    invoked from within
"while 1 {
    incr loop_counter;
    if { $loop_counter > 250 } {
        send_status "connected:no";
        ctrl_exit $ERROR_CONNECTION_TIMEOUT;
   ..."