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mansi gupta 30mansi gupta 30 

exception message='server error returned in unknown format'

Can anyone please help with following error while using the bul api:

exception message='server error returned in unknown format'

we are quering the data from account object and get this error.
can anyone told me how to solve this error.
SwethaSwetha (Salesforce Developers) 
HI Mansi,

This seems to be a network-related issue. Are you behind firewall /proxy?Have you checked with your network team on any changes? Is the issue intermittent or happens all the time? I will be able to suggest better with these details. Thanks
RadekRadek
Hey, I have the same problem. Lately for several processes I am getting ERROR:
 action.AbstractAction handleException (AbstractAction.java:222) - Exception occured during loading
com.salesforce.dataloader.exception.LoadException: Server error returned in unknown format
    at com.salesforce.dataloader.action.visitor.DAOLoadVisitor.handleException(DAOLoadVisitor.java:147)
    at com.salesforce.dataloader.action.visitor.BulkLoadVisitor.handleException(BulkLoadVisitor.java:148)
    at com.salesforce.dataloader.action.visitor.BulkLoadVisitor.loadBatch(BulkLoadVisitor.java:137)
    at com.salesforce.dataloader.action.visitor.DAOLoadVisitor.visit(DAOLoadVisitor.java:105)
    at com.salesforce.dataloader.action.AbstractLoadAction.visit(AbstractLoadAction.java:85)
    at com.salesforce.dataloader.action.AbstractAction.execute(AbstractAction.java:131)
    at com.salesforce.dataloader.controller.Controller.executeAction(Controller.java:173)
    at com.salesforce.dataloader.process.ProcessRunner.run(ProcessRunner.java:156)
    at com.salesforce.dataloader.process.ProcessRunner.run(ProcessRunner.java:107)
    at com.salesforce.dataloader.process.ProcessRunner.main(ProcessRunner.java:266)
Caused by: [AsyncApiException  exceptionCode='ClientInputError'
 exceptionMessage='Server error returned in unknown format'

Does anyone know what could be the reason? 
I read somewhere that upgrading the dataloader to v51 helped, now I have v50.
Could this be the reason?
usama mehboobusama mehboob

Caused by: [AsyncApiException exceptionCode='ClientInputError'     exceptionMessage='Server error returned in unknown format'    ]

I am having the same issue, Is there any update on that? For me it happens intermittently and that is why it is hard to reproduce it on my side. Yes there is a squid proxy running in my environment & all the outgoing requests to salesforce are going through the squid. But if squid was blocking it, it would have blocked all the requests. It happens intermittently or very rarely like 5-10% of time. I am not sure how to debug this. Anyone have any recommendations? thanks