Unable to allocate memory for new incident error in file /u01/app/oracle/diag/rdbms/instance_name/instance_name/trace/instance_name_m72034.trc:
ORA-04036: PGA memory used by the instance exceeds PGA_AGGREGATE_LIMIT
I had a same problem and solved it by doing the following.
See what the current pga_aggregate_limit is using this (in case you want to revert your changes):
show parameter pga_aggregate_limit;
alter system set pga_aggregate_limit = 0;
alter system set pga_aggregate_limit=30348M scope=both;