Hi Alexei,
To help us investigate the problem, please follow the steps below:
1. Run the Fiddler proxy on the client side (that is, on the machine where TestComplete is installed), make TestComplete use Fiddler as a proxy and run your test. Is it the same situation when you run the Fiddler on the IIS side?
2. Try using another web debugger tool instead of Fiddler (for instance, you can use Wireshark). Does the behavior change?
3. Please post here the signature of the method that causes the error message you've mentioned. That is, please provide us with the following information:
3.1. The name of the called method.
3.2. The parameters that belong to this method.
3.3. The values returned by these parameters.
3.4. Your denomination of this method in your test.
Thanks.
