Lookup Field : Invalid data has been used to update the list item. The field you are trying to update may be read only when using Copy.asmx

Hi All,

We are using Copy.asmx in SharePoint to upload files including metadata information. While doing so, we got error for People Picker field as shown below:

Lookup Field : Invalid data has been used to update the list item. The field you are trying to update may be read only.

Resolution:

1. We need to set FieldType for FieldInformation object to User as shown below

2.  Add "-1;#" before User ID

Once this is done, the error disappeared and user id is properly copied to People and Groups field. Hope this helps some one. Cheers!!!