Any ideas on how to go about fixing this?

Lookup the error message in the database(driver) manual or supporting mailing lists, so you know what it means and/or what to do

Then upgrade stuff until it is fixed and/or contact support

For example  [ddg://There is a tds protocol error. An illegal token was received.] There is a tds protocol error. An illegal token was received. -> FIX: SYBASE CT-Library Clients Cannot Connect to Microsoft SQL Server 7.0 says to install a "service pack " on the server, and/or upgrade to newer client libraries

So you'd install new client libraries, then recompile DBD::Sybase to use those new client libraries, and then hopefully the problem goes away