Hello, I have Trados Studio 2017 and following problem: cannot change phase of project, this message apears: "Value cannot be null. Parameter name: key". Thanks in advance for your support. Best

Hello, I have Trados Studio 2017 and following problem: cannot change phase of project, this message apears: "Value cannot be null. Parameter name: key". Thanks in advance for your support. Best
Please check if this KB article applies to your problem:
Trados Studio 2021 SR1 CU3: "Value cannot be null. Parameter name: Key" when translating a Word file (sdl.com)
Or search the knowledge base for this message text, there may be other known error situations with this message.