The Sybase does not allow table row be longer than the page size. Unfortuantely by default the page size is just 2 KB and e.g. See the relathe table that stores variable instances can store strings with size 4000.
This limitation should be documented.

See the related documentation
http://manuals.sybase.com/onlinebooks/group-as/asg1250e/svrtsg/@Generic__BookTextView/15288;pt=15335
http://infocenter.sybase.com/help/index.jsp?topic=/com.sybase.help.ase_15.0.commands/html/commands/commands16.htm
http://infocenter.sybase.com/help/index.jsp?topic=/com.sybase.help.ase_15.0.utility/html/utility/utility203.htm