Problems When Trying To Rebuild Indexex

Hello

I am trying to rebuild indexes on our DB, but I am running into an
error I am not able to solve.

Server: Msg 1105, Level 17, State 2, Line 1
Could not allocate space for object 'ft' in database 'HastaDemo'
because the 'PRIMARY' filegroup is full.
The statement has been terminated.

There is enough diskspace on the disk system, so it must be something
trivial.

Also our DB is heavy on writes, about 2-3 the amount of reads, do you
think a fillfactor of 60 is low enough? I am seing lots of page splits
in perfmon when I used 90% and above, so I am trying to adjust it down
to minimize my pagesplits and thus minimize the Disk I/O, is this the
correct thing to do?

rgds

Matt