Hi Sarah,
We had similar situation (not being able to successfully enter credentilas) and the problem was in the URL we were entering. It is not enough to put only your URL like: https./mycrm.com, but you need to include also following part after CRM domain name: /XRMServices/2011/Organization.svc - at least this was in our case.
You can find more information on this link:
https://community.marketo.com/MarketoArticle?id=kA050000000L7Z0CAKThis is the part you should be looking is following:
Note. Marketo will attempt to access the Dynamics Discovery Service. If it cannot be located, the other option is to look up the Organization Service URL directly in Dynamics. It will have this form:
https://<<organizationURL>>/XRMServices/2011/Organization.svcThis URL can be found in Dynamics by selecting Customizations > Developer Resources. You will want to copy the URL for the Organization Service.
I hope this helps.
We have now a challange in restricting certain leads going from CRM to Marketo. In case you will be having some advices on this part, please let me know.
Thanks, Sara