# Why occur XCTU 0x77 error?

**URL:** <https://forums.digi.com/t/why-occur-xctu-0x77-error/19776>\
**Category:** XBee - WiFi\
**Tags:** xbee-wifi-module\
**Created:** [August 10, 2018, 9:01am UTC](https://forums.digi.com/t/why-occur-xctu-0x77-error/19776 "2018-08-10T09:01:42Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Hamjin](https://avatars.discourse-cdn.com/v4/letter/h/87869e/32.png) [@Hamjin](https://forums.digi.com/u/Hamjin)\
**Post date:** [August 10, 2018, 9:01am UTC](https://forums.digi.com/t/why-occur-xctu-0x77-error/19776/1 "2018-08-10T09:01:42Z")

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Xbee wifi module S6B is trying to send / receive data to other PC using XCTU API mode. However, when data is sent using 0x20 frame type, 0x77 (TCP connection to given IP address and port does not exist. Source port is non-zero so that a new connection is not attempted) error occurs. How can I fix it?  
(However, when AT mode is used, data transmission / reception is good.)