c# - ICloudStorageAccessToken Open says Null reference -

i have problem of opening dropbox folder. code generates exe. when exe executed, starts download package stored in dropbox folder. here code:

    _storage = new cloudstorage();      var dropboxcredentials = new dropboxcredentials();      dropboxcredentials.consumerkey = "xxxxxxxxxxxxxxx";     dropboxcredentials.consumersecret = "xxxxxxxxxxxxxxx";      dropboxcredentials.username = "someusername";     dropboxcredentials.password = "somepassword";      dropboxconfiguration configuration = dropboxconfiguration.getstandardconfiguration();      //open dropbox connection     _storage.open(configuration, dropboxcredentials); 

i sorry have hide confidential information, assume correct. problem occurs @ _storage.open(configuration, dropboxcredentials); says: ![enter image description here][1]

i checked "configuration" , "dropboxcredentials", , not null, , "_storage". confused, problem here exactly? lot.

edit; here stack trace:

at applimit.cloudcomputing.sharpbox.storageprovider.dropbox.dropboxtoken..ctor(oauthtoken token, dropboxbasecredentials basecreds) @ applimit.cloudcomputing.sharpbox.storageprovider.dropbox.logic.dropboxstorageproviderservice.authorizeandgetsession(dropboxcredentials credentials, dropboxconfiguration configuration) @ applimit.cloudcomputing.sharpbox.storageprovider.dropbox.logic.dropboxstorageproviderservice.authorize(dropboxcredentials credentials, dropboxconfiguration configuration) @ applimit.cloudcomputing.sharpbox.storageprovider.dropbox.logic.dropboxstorageproviderservice.createsession(icloudstoragecredentials credentials, icloudstorageconfiguration configuration) @ applimit.cloudcomputing.sharpbox.storageprovider.genericstorageprovider.open(icloudstorageconfiguration configuration, icloudstoragecredentials credentials) @ applimit.cloudcomputing.sharpbox.cloudstorage.open(icloudstorageconfiguration configuration, icloudstoragecredentials credentials) @ webupdater.program.main(string[] args) in c:\\tis\\tools\\webupdater\\webupdater\\program.cs:line 52 @ system.appdomain._nexecuteassembly(assembly assembly, string[] args) @ system.appdomain.executeassembly(string assemblyfile, evidence assemblysecurity, string[] args) @ microsoft.visualstudio.hostingprocess.hostproc.runusersassembly() @ system.threading.threadhelper.threadstart_context(object state) @ system.threading.executioncontext.run(executioncontext executioncontext, contextcallback callback, object state) @ system.threading.threadhelper.threadstart() 

the stack trace shows exception originating inside sharpbox assembly.

a nullreferenceexception indicates kind of bug , such should consider creating issue on sharpbox website.