Input string is not in the correct format at the same time every day

Built a client app that polls the WCF service hosted on IIS7 at timed intervals. I cannot for the life of me understand why I get "Input string is not in the correct format" error at the exact same minute every day, i.e. 4:50am. Checked Event Viewer, nothing there... Is it the SQL Server, VM, network or...?

Here's the error and the StackTrace:

Input string was not in a correct format.  
Server stack trace:     at
System.ServiceModel.Channels.ServiceChannel.ThrowIfFaultUnderstood(Message
reply, MessageFault fault, String action, MessageVersion version,
FaultConverter 开发者_StackOverflowfaultConverter)    at
System.ServiceModel.Channels.ServiceChannel.HandleReply(ProxyOperationRuntime
operation, ProxyRpc& rpc)    at
System.ServiceModel.Channels.ServiceChannel.Call(String action,
Boolean oneway, ProxyOperationRuntime operation, Object[] ins,
Object[] outs, TimeSpan timeout)    at
System.ServiceModel.Channels.ServiceChannelProxy.InvokeService(IMethodCallMessage
methodCall, ProxyOperationRuntime operation)    at
System.ServiceModel.Channels.ServiceChannelProxy.Invoke(IMessage
message)

Exception rethrown at [0]:     at 
    System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage
reqMsg, IMessage retMsg)    at
System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData&
msgData, Int32 type)    at
MyApplication.GenericService.IGenericService.GetCommands(String
fileName, CompanyCredentials credentials, String sequence)    at
MyApplication.GenericService.GenericServiceClient.GetCommands(String
fileName, CompanyCredentials credentials, String sequence)    at
MyApplication.ApplicationClass.RunCommands(String sequence)

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A few things that you could check:

• Are you sending a date time as a string, and there is a diffence in the time format betweem the macines?
• Is recycling of app pool run just before 4:50 so that the first call after recyling allways fails
• How are the credentials being sent? Have the credentials expired?