Oracle 11g not allowing to connect to. Error ORA-01122: database file 1 failed verification check
Did you do anything like renaming datafiles or moving them around in the filesytem?
The ORA-01122 indicates that the information in the controlfile does not match your environment.

So if you do a shutdown/restart of the database and still get the error and moved files around you should move/rename the files to their original places/names and try again.

If all this does not work, have a look at MOS 1041424.6 for details.