Interesting one. Is this specific to this table or other empty ones as well? Which version of sybase are you using.
--do the following
dbcc traceon(3604)
go
dbcc checktable(<table>)
go
dbcc tablealloc (<table>, full,fix)
go
If you still see the same message and the table is empty and you can reverse engineer the table and triggers, then I suggest that you rename the table as follows:
sp_rename <table>, <table_prev>
go
-- create a table with the original name and make sure
-- that you add indexes, primary key and triggers.
--do
update statistics <table>
go
update index statistics <table>
go
sp_recompile <table>
go
and do checktable again.