Description:
As TIBCO Spotfire Data Connectors are client side connectors, they need to be configured on each client that will run analysis using them. This includes the TIBCO Spotfire Web Player server. As such, a file that opens fine within your installed client may not open correctly in the TIBCO Spotfire Web Player server machine if this has not been configured correctly. In this article we will go through one of those cases, where you see the error message: "Sequence contains more than one matching element".
Symptoms:

The following error message can be seen in the TIBCO Spotfire Web Player log file:

ERROR 2016-03-24 11:25:59,097 [plk500v3hkgs3erchupwgw5p, 25484, WorkThread 25,user@domain WAT 1] Spotfire.Dxp.Web.Prompting.PromptHandler+PromptItem - System.InvalidOperationException: Sequence contains more than one matching element
  at System.Linq.Enumerable.SingleOrDefault[TSource](IEnumerable`1 source, Func`2 predicate)
  at Spotfire.Dxp.Data.Access.Adapters.AuthenticationModeService.GetAuthenticationMode(String adapterName)
  at Spotfire.Dxp.Data.Access.Adapters.DataAccessDataSourceLink.NeedsToPromptForCredentials(DataAdapterExecutionContext executionContext, TransientCredentials transientCredentials)
  at Spotfire.Dxp.Data.Access.Modeling.ManagedDataConnection.<PromptForCredentials>d__5.MoveNext()
  at Spotfire.Dxp.Data.DataManager.<LoadDataTables>d__93.MoveNext()
  at Spotfire.Dxp.Data.DataManager.<LoadData20AndLater>d__4c.MoveNext()
  at Spotfire.Dxp.Data.DataManager.<LoadDataCore>d__38.MoveNext()
  at Spotfire.Dxp.Data.DataManager.<LoadData>d__1f.MoveNext()
  at Spotfire.Dxp.Application.PartiallyOpenedDxpFile.<LoadData>d__0.MoveNext()
  at Spotfire.Dxp.Application.AnalysisApplication.<OpenPartiallyOpenedDocument>d__34.MoveNext()
  at Spotfire.Dxp.Web.WebAnalysis.<Open>d__bc.MoveNext()
  at Spotfire.Dxp.Web.WebAnalysis.<OpenFromCache>d__c4.MoveNext()
  at Spotfire.Dxp.Web.WebAnalysis.<OpenWithProgress>d__e0.MoveNext()
  at Spotfire.Dxp.Web.Prompting.PromptHandler.PromptItem.PromptNext()
  at Spotfire.Dxp.Web.Prompting.PromptHandler.PromptItem.Execute()
ERROR 2016-03-24 11:25:59,159 [plk500v3hkgs3erchupwgw5p, 25484, WorkThread 25, user@domain WAT 1] Spotfire.Dxp.Web.WebAnalysis - Unable to open file '/folder/Analysis'
System.InvalidOperationException: Sequence contains more than one matching element
  at System.Linq.Enumerable.SingleOrDefault[TSource](IEnumerable`1 source, Func`2 predicate)
  at Spotfire.Dxp.Data.Access.Adapters.AuthenticationModeService.GetAuthenticationMode(String adapterName)

The section mentioned looks like the following.

      <setting name="WebAuthenticationMode" serializeAs="Xml">
        <value>
          <adapters>
            <adapter name="Spotfire.SqlServerAdapter" mode="Prompt" />
            <adapter name="Spotfire.TeradataAdapter" mode="Prompt" />
            <adapter name="Spotfire.OracleAdapter" mode="Prompt" />
            <adapter name="Spotfire.SsasAdapter" mode="Prompt" />
            <adapter name="Spotfire.SapBwAdapter" mode="Prompt" />
            <adapter name="Spotfire.EssbaseAdapter" mode="Prompt" />

            <adapter name="Spotfire.CompositeAdapter" mode="Prompt" />

            ...
          </adapters>
        </value>

The issue can be seen if one by mistake adds the same adapter twice, for example:

      <setting name="WebAuthenticationMode" serializeAs="Xml">
        <value>

          <adapters>

            <adapter name="Spotfire.SsasAdapter" mode="Kerberos" />

            <adapter name="Spotfire.SqlServerAdapter" mode="Prompt" />
            <adapter name="Spotfire.TeradataAdapter" mode="Prompt" />
            <adapter name="Spotfire.OracleAdapter" mode="Prompt" />
            <adapter name="Spotfire.SsasAdapter" mode="Prompt" />
            <adapter name="Spotfire.SapBwAdapter" mode="Prompt" />
            <adapter name="Spotfire.EssbaseAdapter" mode="Prompt" />

            <adapter name="Spotfire.CompositeAdapter" mode="Prompt" />

• Spotfire.Dxp.Worker.Host.exe.config file, TIBCO Spotfire® Server and Environment - Installation and Administration manual
  • https://docs.tibco.com/pub/spotfire_server/11.4.5/doc/html/TIB_sfire_server_tsas_admin_help/server/topics/spotfire.dxp.worker.host.exe.config_file.html