ora-27102 error occurring in the middle of the tests

Hi we are using oracle 11gR1 (11.1.0.7) on SuSE Linux. We have 4GB memory and 2GB allocated to oracle. The swap space available is 4GB. When we are running tests in the middle of the tests the ORA-27102 error is occurring. I cannot find this error in the alert log but the application people can see this error in their serverlog.
Total System Global Area 2071076864 bytes
Fixed Size                  2161232 bytes
Variable Size            1375733168 bytes
Database Buffers          687865856 bytes
Redo Buffers                5316608 bytes

oracle@perf:~> swapon -s
Filename                                Type            Size    Used    Priority
/dev/sda5                               partition       4200956 976196  -1

cat /proc/meminfo
MemTotal:      4048976 kB
MemFree:        126176 kB
Buffers:         20212 kB
Cached:        1871208 kB