Solr JSON Facet API Response

{
  "responseHeader":{
    "status":400,
    "QTime":3,
    "params":{
      "df":"text",
      "debug":"true",
      "json.nl":"map",
      "indent":"true",
      "echoParams":"all",
      "fl":"project_titles_txt",
      "fq":["geo_coords:[22.258,84.8884 TO 22.258,84.8884]",
        "bundle:pop_sample",
        "has_abundance_data_b:true",
        "has_geodata:true",
        ""],
      "rows":"1",
      "q":"*:*",
      "json":"{\"filter\":[\"bundle:pop_sample\",\"has_abundance_data_b:true\",\"has_geodata:true\",\"\"],\"facet\":{\"term\":{\"type\":\"terms\",\"limit\":-1,\"field\":\"species_category\",\"facet\":{\"collection_dates\":{\"type\":\"terms\",\"limit\":-1,\"field\":\"collection_date\",\"facet\":{\"collection\": {\"type\":\"terms\",\"field\":\"collection_assay_id_s\",\"facet\":{\"abnd\":\"sum(div(sample_size_i, collection_duration_days_i))\"}}}}}}}}",
      "term":"species_category",
      "wt":"json",
      "facet":"true"}},
  "response":{"numFound":4,"start":0,"docs":[
      {
        "project_titles_txt":["Increasing the potential for malaria elimination by targeting zoophilic vectors"]}]
  },
  "facet_counts":{
    "facet_queries":{},
    "facet_fields":{},
    "facet_ranges":{},
    "facet_intervals":{},
    "facet_heatmaps":{}},
  "error":{
    "metadata":{
      "error-class":"org.apache.solr.common.SolrException",
      "root-error-class":"org.apache.solr.common.SolrException"},
    "msg":"Invalid Date String:'Fri Aug 01 00:00:00 UTC 2014'",
    "code":400}}