error reading from salesforce adapter [BODS]

i have a requirement to read data from salesforce to SQL database.

ETL being BODS.

BODS job is very simple: direct mapping of source to target fields.

the job loads successfully in DEV. but only in QTY, the job fails most of the times with below error message.

error message from the job monitor:

Error reading from <SALESFORCE_SOURCE_TABLE>:

<Could not read data for session 67, operation 66 (Adapter: 'SalesForce')>

but when our basis team checks the salesforce adapter logs,

there are no error messages.

also the salesforce adapter is in green and stable status.

settings for salesforce adapter in DEV is : 1GB

settings for salesforce adapter in QTY is : 2GB

please suggest your views.