Today we experienced the following message in Azure Portal
WebJob cannot be added from portal if deployment form source control is configured.
The workaround that worked for me was uploading the webjob directly via the Kudu Console.
Open the Kudu Console by selecting "Advanced Tool" --> "Go" in Your App Service on the Azure Portal.
Once on the Kudu portal open a "Debug Console" --> "CMD"
Go to the directory for your webjobs: "d:\home\site\wwwroot\app_data\jobs\continuous\{job name}" (https://github.com/projectkudu/kudu/wiki/WebJobs)
Then drag and drop the .zip file you prepared to upload your webjob (https://github.com/projectkudu/kudu/wiki/Kudu-console)
The job will now be listed on the Azure Portal and be started.