ExecuteError: Failed to execute. Parameters are not valid.
ERROR 000800: The value is not a member of [list of values]

class SetLayer(object):
    """Implementation for leetScripts_addin.button2 (Button)"""
    def __init__(self):
        self.enabled = True
        self.checked = False
    def onClick(self):
        self.a = pythonaddins.GetSelectedCatalogWindowPath()
        self.a = self.a.encode('mbcs')
        print self.a
        self.b = os.path.split((self.a))
        self.c = self.b[0]
        self.d = os.path.split(self.c)
        self.e = (self.b[1]) #feature class
        self.f = (self.d[1]) #feature dataset
        self.g = (self.d[0]) #workspace
        print "Feature class: %r" % self.e
        print "Feature dataset: %r" % self.f
        print "Workspace: %r" % self.g
        connProp = arcpy.Describe(self.g).connectionProperties
        self.h = connProp.instance.split(":", 2)
        self.k = self.h[2].encode('mbcs') #instanceX
        self.i = connProp.database.encode('mbcs') #databaseX
        print "Instance is %r" % self.k
        print "Database is %r" % self.i
        print "Availible Versions:"
        self.List = arcpy.da.ListVersions(self.g)
        self.nameList = []
        for version in self.List:
            self.nameList.append(version.name)

        print self.nameList
        print "Tool finished"
        pass

#working on editing this to provide dropdown
class setVersion(object):
    """Implementation for leetScripts_addin.combobox2 (ComboBox)"""
    def __init__(self):
        self.editable = True
        self.enabled = True
        self.width = 'WWWWWW'*3
        self.dropdownWidth = 'WWWWW'*3
    def onEnter(self):
        self.items = button2.nameList
    def onSelChange(self, selection):
        #self.items.append(button2.nameList)
        self.version = selection#change this
        print self.version
        pass

if sde != -1 and desc.isVersioned:

            #Check to see if this connection file exists
            path = r"U:tempStuffactualName.sde"
            if not os.path.isfile(path):
                #Creates connection file if it doesn't already exist
                os.makedirs(r"U:tempStuff")
                outFolderPath = r"U:tempStuff"
                outName = r"actualName.sde"
                databasePlatform = "SQL_Server"
                instance = button2.k
                database = button2.i
                username = "username"
                password = "password"
                version = combobox2.version
                #Make sure you change between OPERATING_SYSTEM_AUTH and DATABASE_AUTH
                arcpy.CreateDatabaseConnection_management(outFolderPath, outName,
                                                          databasePlatform,
                                                          instance,
                                                          'OPERATING_SYSTEM_AUTH',
                                                          username, password,
                                                          'DO_NOT_SAVE_USERNAME',
                                                          database,
                                                          '','TRANSACTIONAL',
                                                          version,'')

            workspace = r"U:tempStuffactualName.sde"#change to current workspace
            fc = os.path.join(workspace, featureDataset, fcName)
            print workspace
            print "Feature class is %r" % fc
            #Start editing
            print "initiating editing"
            arcpy.ChangeVersion_management(fcName, "TRANSACTIONAL",
                                           combobox2.version, '')