Hi,
We are having the same issue, if you turn off custom error pages the exception is:
Specify a default search provider.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.Configuration.Provider.ProviderException: Specify a default search provider.
The global search is working but the search within ideas not. Does anyone have any experience to solve this?