M340 firmware 3.01 and up does not consistently connect with Unity V7.0

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Issue
I loaded a BMXP342020 with v3.01 firmware and used Unity Pro V7.0 running on WIN XP to load a program to it.
After I disconnect, I can successfully test connection but can not connect. I always get an Error during connect message.
If I power down, remove the SD card and power up, I can connect, transfer, put into run.. but then if I disconnect, can not reconnect.
Downgrading to v2.90 allows connections to work fine with Unity V7.

Product line
Modicon M340

Resolution
R&D identified the root cause of this issue and it was fixed in the M340 fw v3.30.
This issue was due to the length of the frame sent by Unity Pro v7 (and lower version) which was too long. The fix is to upgrade the M340 to the latest version of firmware found at https://www.se.com/us/en/search/M340 .