I was helping a customer set up hybrid search, when we ran into a frustrating issue. We'd run the hybrid picker, choose hybrid search only, enter the parameters, and say create. The picker would kick off, and then fail quickly, with the message "Parameters too long or contain forbidden character."
2018.01.03 15:15:31.977 *ERROR* [Workflow=Hybrid, Task=HybridSearchConfiguration, Phase=Configure] System.Exception: Parameters too long or contain forbidden character.
at Microsoft.Online.CSE.HybridSP.StandardWorkflow.HybridSearchTask.ConfigureHybridSearch()
at Microsoft.Online.CSE.HybridSP.StandardWorkflow.HybridSearchTask.Configure()
It turns out that our issue was that the Online Services Sign-In Assistant and Azure Active Directory PowerShell modules were not installed on the TARGET servers, where hybrid search was to be deployed. There's a checkbox in the wizard that says they're installed, but it's not specific as to which boxes. Be careful!