Detailed error

{
  "Date": "2017-12-12T18:20:29.8496167+00:00",
  "Message": "Some artifacts collide on unique identifiers.\r\nThis means that they have different Udis, yet\r\nthey refer to the same unique Umbraco object\r\nand therefore cannot be processed.\r\n---------------------------------------------\r\nCollisions for entity type \"relation-type\": \r\n  Collisions for unique identifier \"nexuDocumentToDocument\":\r\n    Artifact: umb://relation-type/1367ade7d52344c1a43a4dacaf55ee0f\r\n    {RelationType umb://relation-type/4e977e35af193517b79b42dcf7efa139}\r\n",
  "Ex": {
    "ClassName": "Umbraco.Deploy.Exceptions.ArtifactCollisionException",
    "Message": "Some artifacts collide on unique identifiers.\r\nThis means that they have different Udis, yet\r\nthey refer to the same unique Umbraco object\r\nand therefore cannot be processed.\r\n---------------------------------------------\r\nCollisions for entity type \"relation-type\": \r\n  Collisions for unique identifier \"nexuDocumentToDocument\":\r\n    Artifact: umb://relation-type/1367ade7d52344c1a43a4dacaf55ee0f\r\n    {RelationType umb://relation-type/4e977e35af193517b79b42dcf7efa139}\r\n",
    "Data": null,
    "InnerException": null,
    "HelpURL": null,
    "StackTraceString": "   at Umbraco.Deploy.ServiceConnectors.RelationTypeConnector.ProcessInit(RelationTypeArtifact art, IDeployContext context)\r\n   at Umbraco.Deploy.ServiceConnectors.ServiceConnectorBase`3.ProcessInit(IArtifact art, IDeployContext context)\r\n   at Umbraco.Deploy.Environments.LocalUmbracoEnvironment.<>c__DisplayClass26_0.<ProcessArtifacts>b__0(IArtifact x)",
    "RemoteStackTraceString": null,
    "RemoteStackIndex": 0,
    "ExceptionMethod": "8\nProcessInit\nUmbraco.Deploy, Version=2.0.9.0, Culture=neutral, PublicKeyToken=null\nUmbraco.Deploy.ServiceConnectors.RelationTypeConnector\nUmbraco.Core.Deploy.ArtifactDeployState`2[Umbraco.Deploy.Artifacts.RelationTypeArtifact,Umbraco.Core.Models.IRelationType] ProcessInit(Umbraco.Deploy.Artifacts.RelationTypeArtifact, Umbraco.Core.Deploy.IDeployContext)",
    "HResult": -2146233088,
    "Source": "Umbraco.Deploy",
    "WatsonBuckets": null
  },
  "Sender": "Umbraco.Deploy.WorkItems.DiskReadWorkItem"
}

Error message

Some artifacts collide on unique identifiers.
This means that they have different Udis, yet
they refer to the same unique Umbraco object
and therefore cannot be processed.
---------------------------------------------
Collisions for entity type "relation-type": 
  Collisions for unique identifier "nexuDocumentToDocument":
    Artifact: umb://relation-type/1367ade7d52344c1a43a4dacaf55ee0f
    {RelationType umb://relation-type/4e977e35af193517b79b42dcf7efa139}