I noticed you posted what appeared to be this same issue in the STB forum, so here are 2 responses depending on what game forum you meant to post in
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If this is for STB2002: Check to make sure all the folders are there - you need a BOX, EXPIMP, LOGOS, and NEWS folder within your league folder.
If this is for OOTP4: Check to make sure all the files are there is incomplete. The league folder should contain these files:
Coaches.dat
league.dat
park.dat
parkconfig.dat
Players.dat
promos.dat
schedule.dat
special.dat
teams.dat
teams2.dat
weather.dat
If the league has already started then chances are the following files should be in the league folder as well:
draft.dat
messages.dat
records.dat
scouting.txt
Spring.dat
story.dat
trade.dat