HTTP Error 400. The size of the request headers is too long

Our company has purchased the UiPath Orchestrator standalone version and the official license. However, we suddenly encountered an unknown error during login today, and we are unable to troubleshoot the issue. We need to seek assistance from the official technical team.

1.unknown error (code:200) when login in UiPath Identity Server
2.Bad Request - Request Too Long
HTTP Error 400. The size of the request headers is too long.

Try the or installers.

If you have Windows Auth implemented, this should resolve the issue.

By default, there is no MaxFieldLength registry entry. This entry specifies the maximum size limit of each HTTP request header. The MaxRequestBytes registry entry specifies the upper limit for the total size of the Request line and the headers. Typically, this registry entry is configured together with the MaxRequestBytes registry entry.

If the MaxRequestBytes value is lower than the MaxFieldLength value, the MaxFieldLength value is adjusted. In large Active Directory environments, users may experience logon failures if the values for both these entries aren’t set to a sufficiently high value.

The MaxFieldLength and MaxRequestBytes registry keys are located at the following sub key:


Set the key values as shown in the following table:

Name - MaxFieldLength

Value Type - DWORD

Value Data - 65536

Name - MaxRequestBytes

Value Type - DWORD

Value Data - 16777216

Refer to the below screenshots:

Create both the parameters with the above mentioned Value Data, then restart the Orchestrator server.

Note: Before changing registry, request to take the backup of registry.

Reference: HTTP 400 error responses to HTTP requests - Internet Information Services | Microsoft Learn

If not, please review this article

The problem has been resolved. Thank you for your timely support