Hello, rather than opening a new thread, I'm having this very same issue.
I got promoted with Sestao to Spanish 2nd tier, I have renewed some players and signed some new ones and all was fine.
However now during the winter trasnfer window, I cannot sign anyone - despite having 250K (per year) of free space in the wages budget, I can only offer 66K to Star players, 45K to important and so on.
This makes it hard to sign players, but abvove all as in the Second Division there is a rule that its not possible to register players who are on less than 77K / year, even if someone would accept the wages, I could have them registered for first team.
If you need, I can upload you my saved game.