batched calls to web services

Hello all,

we have a user interface page that makes multiple calls to a web service. We have been getting following error lately

System.InvalidOperationException-- Collection was modified; enumeration operation may not execute.

after much debugging it looks like this might be caused by multiple threads accessing the service the service at the same time, and it also looks like asp.net ajax is batching server calls together. I am wondering if its making calls to the same instance of the webservice.

to force serialization i put a javascript alert between service calls, and it fixes the issue,

 I am wondering if someone else has faced similar problem, and if there is anything that can done about it.

 Thanks
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