BFGminer won't work any longer on Testnet

Hello All,

Hope I don't break any rule, as this is my first post on this forum.

Does someone has a idea on this problem :
I'm running a full node Bitcoin Core v0.13.0 (64-bit) with BFGminer 5.4.2-win64 on the same computer.
Starting as : bfgminer.exe --stratum-port=3333

I connect with 2 Antminer S1's to BFGminer.

All seems working fine for the real Bitcoin network but NOT (no longer ) for the testnet.
Alltrough it worked fine before and only Testnet=1 needs tot be changed in the Bitcoin.conf

BFGminer keeps complaining :
Pool 0 slow/down or URL or credentials invalid.
No servers were found that could be used to get work from

If I remove Testnet=1 from the config and start again, no longer complains.

Would this has to do something with the 'versionbit 28' in use for the moment on the testnet ?
And if so, what can I do about it ?

Thanks for all reply's !

Kind regards.