Fixing Win32 Error 0x000006A8 (RPC_S_INVALID_RPC_PROTSEQ)

The error code 0x000006A8 translates to RPC_S_INVALID_RPC_PROTSEQ. This error message indicates an issue with the RPC protocol sequence specified in the binding string used for a Remote Procedure Call (RPC) connection.

Understanding Invalid RPC Protocol Sequences:

• RPC communication protocols can be chained together in a sequence for specific purposes. For example, a sequence might use TCP for the underlying transport and then use another protocol like DCE-RPC on top of TCP.
• The RPC_S_INVALID_RPC_PROTSEQ error occurs when the binding string specifies an invalid or unsupported protocol sequence for the RPC connection.

Reasons Behind RPC_S_INVALID_RPC_PROTSEQ:

There are a couple of reasons why you might encounter this error:

• Incorrect Protocol Sequence: The binding string might be using a combination of protocols that are not compatible with each other or not supported by the remote service.
• Outdated or Incorrect Configuration: The program or service configuration on either your computer or the remote system might be outdated and not configured for the desired protocol sequence.

Resolving RPC_S_INVALID_RPC_PROTSEQ:

1. Review Binding String Protocol Sequence:

   • Carefully examine the binding string to identify the protocol sequence specified. Consult the documentation for the remote service to see if it supports that specific sequence.

2. Verify Program or Service Configuration (if applicable):

   • If you have access to the configuration settings of the program or service on either your computer or the remote system, see if there are options to specify the communication protocol sequence for RPC connections.

3. Software Vendor Support:

   • If you’re unsure about the supported protocol sequences or encounter configuration issues, consider reaching out to the software vendor’s support for the program or service you’re trying to access remotely. They can provide information on supported protocol sequences and how to establish a compatible RPC connection.

4. Simplify Protocol Sequence (if possible):

   • In some cases, using a simpler protocol sequence (like a single protocol instead of a sequence) might be possible. Explore if the program or service you’re using allows specifying a basic supported protocol for the RPC connection.

Additional Tips:

• RPC tools or libraries might offer features to automatically negotiate the protocol sequence with the remote service. Consider using such tools if available to simplify the connection process.
• If you manage network configurations, ensure that the necessary ports for the individual protocols within the sequence are open for communication between your computer and the remote system.

By understanding the concept of RPC protocol sequences and the reasons behind the RPC_S_INVALID_RPC_PROTSEQ error, you can identify the invalid protocol sequence issue. Reviewing the binding string protocol sequence, verifying program or service configuration (if applicable), consulting software vendor support, simplifying the protocol sequence (if possible), and checking network configurations are some recommended steps to address this error.