Hi!
wallet.dat is a file that houses a database. The database format of various versions of Syscoin is incompatible with one another.
This means you need to open that wallet.dat in the version of Syscoin that created it (or a compatible one), then dump your private keys and import them into one of the current Syscoin clients.
The process is described in
but should work analog (with little changes) for any version of Syscoin. Nonetheless, if the wallet.dat belongs to an earlier version, please tell us before you attempt the process… and always keep a backup 