I don't speak spanish, sadly...
But if I understand you right, the contracts of the riders expire on the first day(s) of a new career with a certain 2007 DB.
You can download the Converters for CyM4 (Download section -> CyM4 -> Editors & Utilities); here you need the converter for the DYN_contract_cyclist.
Use the converter to convert this part of the DB into a *.txt-file named DYN_contract_cyclist.txt.
Open this file and change the 5th column: If you want all contracts to expire in 2007, insert 1193310000. If you want a contract to expire in 2008, insert 1224846000 instead.
After doing this, import the txt-file into the DB again using the converter. Now it should work, as far as I know.
Maybe someone can translate this to spanish?