When does the error occur?
The error occurs when you are trying to associate your TestComplete project’s test case with a test case, which is managed by Azure DevOps or Team Foundation Server, via the Associate with Azure DevOps / TFS Test Cases wizard.
Why is the message shown?
The message is shown because the string you have specified in the The ID of the Azure DevOps / TFS test case to add text box of the wizard is not a proper ID of an Azure test case. A test case ID must be an integer value.
Workarounds
Type a proper ID in the The ID of the Azure DevOps / TFS test case to add text box or click the ellipsis button of the text box and select the needed test case in the Choose Test Case dialog.