The number of login users has reached the limit.

[tomasenskede]

When I try to setup this connection I get this error:

when I try to access the same swtich via an brower I get this error:

Why does it get locked when I try to connect it with HA?

My switch;

[schariwari]

Same Issue her, but have some additional Info as I have two of the TL-SG1016DE:

The older one with the Hardware-Release 1.0 (the same as you have) has a the newest available firmware from 2013 (!) and have the same issue than you.
The other, newer one has HW-Release 4.0 (and also a newer Firmware from 2019) is working well with the intergration, can login and get some information (IP-Adress, Port Connected/Not Connected, Ports can be switched On/Off, but not Port-Statistic and certainly no POE-Info as this switch does not support this).

TP-Link Website strictly warns to update a V4-firmware to a V1-Hardware so I did not want to go the risk of bricking the switch.

Another additional info: I own also a TL-SG108E, HW-Version 6.0 with Firmware from 2023, which also works exactly like the newer of the 16-port-switches.