ORA-12838: cannot read/modify an object after modifying it in parallel

User try to open PO period, users got the error ORA-12838: cannot read/modify an object after modifying it
in parallel.

system error : Bug 28039754 : OPEN PERIOD ERROR ORA-12838

PROBLEM STATEMENT
=================
Open period first period of 2018 Error :
gl_summary_account_types_pkg.update_account_types() 
SHRD0114: Executing Pro*C statement Update acct type...

SHRD0043: ERROR: ORA-12838: cannot read/modify an object after modifying it
in parallel

Solution:  

1. make sure gl.gl_code_combinations is not parallel.

2.  Make sure your GL period is open.

3. finally open the PO period.

Workflow diagram unable to view

Please make sure your Java certificate up to date.
$OA_JRE_TOP

How to check the cluster Verification

./crsctl check crs

CRS-4638: Oracle High Availability Services is online

CRS-4537: Cluster Ready Services is online

CRS-4529: Cluster Synchronization Services is online

CRS-4533: Event Manager is online