E_BAD_CREDENTIALS_ERROR sometimes happened during BOCS file upload ( uploadDistributedContent )

[jbleeok]

I have 4 acs servers and one bocs server.
At first, I thought long no-action on bocs and acs produce 401 error.
But now, I think it's random.
I create and remove a document every 10 minutes with distributed write through bocs server and it failed sometimes with exception :

[error] status [401]
[error] code [null]
[error] message [{"status":401,"code":"E_BAD_CREDENTIALS_ERROR","message":"Authentication failed because an invalid credential is provided.","details":"(DM_SESSION_E_AUTH_FAIL) [DM_SESSION_E_AUTH_FAIL]error: "Authentication failed for user jinbae8663.lee with docbase semdoc."","id":"c266d178-09ac-40c5-8f59-740a53769ef2"}]
[error] detail [null]
[error] id [null]
12:24:35.910 [scheduled-executor-thread-5] ERROR i.m.s.DefaultTaskExceptionHandler - Error invoking scheduled task for bean [com.sec.controller.BocsController@f0cabd7] null
com.emc.documentum.rest.client.sample.client.DCTMRestErrorException: null
at com.emc.documentum.rest.client.sample.client.impl.AbstractRestTemplateClient.uploadDistributedContent(AbstractRestTemplateClient.java:481)
at com.sec.controller.BocsController.makeDocAndRemove(BocsController.java:562)