Too many open files - Isam error 104

Hi all, we have an Informix-4ge program that stops with error 104 "too many open files" while trying to open a violation table. Same program has run for years without this error. The code has not been changed. The schema of two tables has changed: stop violations table for xxx_neu; drop table xxx_neu_vio; drop table xxx_neu_dia; alter table xxx_neu add (verarb_status SMALLINT); start violations table for xxx_neu; set indexes xxx_n_1 filtering; alter table yyy_neu add (anmelde_grund CHAR(2), abmelde_grund CHAR(2), svs67 CHAR(2)); Those columns are not in use of the program yet. Parts of the program runs on new application server (Solaris 10 Zone). May be the pogram runs faster than before. The Informix Server is 11.50FC7W3. OS is Solaris 10. We checked some limits on the appservers and the database server host. Ulimit is set to 256 for the appusers and for user informix before starting the databaseserver. We couldn't see many open files on the appserver. The informix databaseserver has more than 3000 concurrent sessions, most of them ontlitcp connections. What would you suggest? TIA, Reinhard.