Bad request 400 Error when using parent cache node

I'm trying to design a load balancing system with a parent cache. I have 2 Child Cache servers with ARR and Network load balancing features installed. (vServer2008-1: 10.7.10.90, vServer2008-3:10.7.10.91). When i setup the Network Load Balancing feature i gave it the virtual IP 10.7.10.80. I have 1 Parent Cache Server (vServer2008-2). The problem is; when i try to reach the app servers with the http://10.7.10.80/App IP, i have the "Bad Request 400" Error. If i use http://vServer200-1/App it works with no problem. And if i use the http://10.7.10.90/App, again i have the bad request error. I have enabled the failed request tracing feature for the iis. The exact message is like this;

ModuleName ApplicationRequestRouting 
Notification 128 
HttpStatus 400 
HttpReason Bad Request 
HttpSubStatus 0 
ErrorCode 0 
ConfigExceptionInfo  
Notification EXECUTE_REQUEST_HANDLER 
ErrorCode The operation completed successfully. (0x0) 

Any ideas? Thx in advance...