Mirador viewer

SyntaxError: Unexpected token '<', "<!DOCTYPE "... is not valid JSON

{
  "manifest": {
    "error": "SyntaxError: Unexpected token '<', \"<!DOCTYPE \"... is not valid JSON",
    "id": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/741/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-76a9769e-a648-4fd4-a53d-b4519eed56c9",
      "cw-6e8449a5-b749-4541-b3f3-c53a4b86a8d2"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-b12a7458-4b66-4286-8dbb-a1ec2d1fde0d",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/741/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-6e8449a5-b749-4541-b3f3-c53a4b86a8d2"
  }
}