Hello,
We have a SOAP webservice that sometimes returns this error:

We are trying to install "Force.com IDE 2. The Eclipse IDE plug-in for Salesforce DX" and we follow all the steps include in the guide:
https://developer.salesforce.com/docs/atlas.en-us.sfdx_setup.meta/sfdx_setup/sfdx_setup_intro.htm

But when I try to 'Pull the Source' an error ocurred:
    Operation Failed

    MemberName, IsNameObsolete FROM SourceMember WHERE RevisionNum >
                                ^
    ERROR at Row:1:Column:52
    sObject type 'SourceMember' is not supported. If you are attempting to use a custom object, be sure to append the '__c' after the entity name. Please reference your WSDL or the describe call for the appropriate names.

And there is no way to continue.