Found the cause of the Invalid data frame I've been getting:
Oct 08 06:58:12 FIDOPOLL Version 1.12 A35
Oct 08 06:58:12 Scanning 21:1/145
Oct 08 06:58:12 Queued 0 files (0 bytes) to 21:1/145
Oct 08 06:58:12 Polling BINKP node 21:1/145
Oct 08 06:58:12 Connecting to 10.0.0.21:24556
Oct 08 06:58:12 Connected
Oct 08 06:58:12 Invalid data frame
Oct 08 06:58:12 Recv: Data 8/16,972
Oct 08 06:58:12 Authorization State: 1 HH:0 NH:1
Oct 08 06:58:12 Remote disconnect
Oct 08 06:58:12 Authorization failed
Oct 08 06:58:12 FIDOPOLL Version 1.12 A35
Oct 08 06:58:12 Scanning 80:603/0
Oct 08 06:58:12 Queued 0 files (0 bytes) to 80:603/0
Oct 08 06:58:12 Polling BINKP node 80:603/0
Oct 08 06:58:12 Connecting to 10.0.0.21:24556
Oct 08 06:58:12 Connected
Oct 08 06:58:12 Invalid data frame
Oct 08 06:58:12 Recv: Data 8/16,972
Oct 08 06:58:12 Authorization State: 1 HH:0 NH:1
Oct 08 06:58:12 Remote disconnect
Oct 08 06:58:12 Authorization failed

It had this failure with Linux x64 and Windows10 x64 (dual boot), so I
checked badip.txt again and found it on the Hub. Deleted it and added 10.0.*
to the goodip.txt and whitelist.txt (so it won't happen again) and then
polling worked. So Invalid data frame can be the result of badup.txt or blacklist.txt, if your getting them have the hub feeding you checked for your IP in badip.txt and blacklist.txt and have them put in goodip.txt and whitelist.txt and the problem shouldn't appear again.

--- Mystic BBS v1.12 A35 (Raspberry Pi/32)
* Origin: Mystic Pi BBS bcw142.zapto.org (21:1/145)

On 10/08/17, bcw142 pondered and said...

It had this failure with Linux x64 and Windows10 x64 (dual boot), so I checked badip.txt again and found it on the Hub. Deleted it and added 10.0.* to the goodip.txt and whitelist.txt (so it won't happen again)
and then polling worked. So Invalid data frame can be the result of badup.txt or blacklist.txt, if your getting them have the hub feeding
you checked for your IP in badip.txt and blacklist.txt and have them put in goodip.txt and whitelist.txt and the problem shouldn't appear again.

Good info thanks :) Something I was aware of through past experiences but
good to have it noted here too :)

Best, Paul

--- Mystic BBS v1.12 A35 (Windows/32)
* Origin: Agency BBS | telnet://agency.bbs.geek.nz (21:1/101)