semaphore-sets and oracle7

I have following problem:
On my system (IRIX 6.0.1) its only possibe to run 60 oracle-processes alltogether for example:
i start the first database ork1 with the parameter processes=25 then i start the second database ork2 with the parameter processes=20 then i start the third database ork3 with the parameter processes=15 that works well but I cant start a fourth database ork4 with the parameter processes= 10 because I get the error messageora-07279 ....unable to get first semaphore set. Only when I decrease the process paramter from ork2 to processes=10 the fourth database works. When Im manipulating the parameters its always the same. Is the sum of all 4 process-parameters 60 the 4 databases were starting up well.

The system-parameters are SEMMNI=60 SEMMSL=60 SEMMNS=60. Is anybody so kind to explain me this problem?

    Thanks a lot

                   Michael