I'd suggest a couple options:
----------------------- option #1
Your *fmt file is likely not correct. "Duh, Mark!" ?
NOTE: I don't normally use format files so I don't recall (off the top of my head) the proper/correct format of the *fmt file, so short of re-reading the manuals I use the following method to generate a properly/correctly formatted *fmt file:
- use the INSERT command to populate the Sybase table with a few of your data values (4-digit, 5-digit, 8-digit, etc)
- use bcp to pull the data from your table and have bcp create the *fmt file for you
- try using the *fmt file (created by bcp/out) to bcp your data file into the table
----------------------- option #2
Since your data file is just integers with a <lf>, consider skipping the format file ...
bcp dbname.owner.TO_INTS in "SomeInts.txt" -P password -S server -U sa -c -r "\n" -e "bcp.errlog.txt"
The -r option allows you to designate the row delimiter.
NOTE: To be honest I don't recall (off the top of my head, again) if <lf> is '\n' or '\r' or '\n\r' or '\r\n', so try each to see which works best. I usually use the UNIX 'od' command to verify the line terminator. I'd suggest using a small file (eg, 5-10 values) to make sure you've got the right -r setting before trying to load a huge data set.
NOTE: The -t option allows you to define the column delimiter, eg, -t '\t' says you've got a tab between each column.