Once again, I can't upload photos because they are "too big".

[SatNavSaysStraightOn]

1600px by 1200px

Those dimension are fine for the media gallery as you say but madebyyouandi is not using it (yet) so will need to follow the smaller dimensions of 1200×1024 for direct in post file attachments.

 

[CookieMonster]

some forum software accepts anything and resizes as needed....
just saying.