I keep getting the following error during a site import:

ERROR: Error importing 'Document types' objects (Default product)
Message: [DataConnection.ExecuteQuery]: Query: ALTER TABLE Custom_DefaultProduct ADD [ProductName] nvarchar(200) NOT NULL CONSTRAINT DEFAULT_Custom_DefaultProduct_ProductName DEFAULT '': caused exception: Cannot find the object "Custom_DefaultProduct" because it does not exist or you do not have permissions. Stack Trace: at CMS.DataProviderSQL.DataConnection.ExecuteQuery(String queryText, QueryDataParameters queryParams, QueryTypeEnum queryType, Boolean requiresTransaction)
at CMS.SettingsProvider.SqlHelperClass.ExecuteQuery(QueryParameters query, IDataConnection conn)
at CMS.DataEngine.AbstractTableManager.AddTableColumn(String tableName, String columnName, String columnType, Boolean allowNull, String defaultValue)
at CMS.DataEngine.TableManager.CreateTableBySchema(String tableName, String schema)
at CMS.CMSImportExport.ImportProvider.UpdateObject(SiteImportSettings settings, GeneralizedInfo infoObj, Boolean siteObject, DataSet ds, TranslationHelper th, Boolean updateChild, Int32 targetSiteId, ProcessObjectEnum process, Dictionary`2 importedParentIDs, List`1 postProcessList, List`1 affectedObjects, BaseInfo parentObject)
at CMS.CMSImportExport.ImportProvider.ImportObjects(SiteImportSettings settings, DataSet ds, String objectType, Boolean siteObjects, TranslationHelper th, Boolean importChild, ProcessObjectEnum processType, Dictionary`2 importedParentIDs) at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection)
at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning()
at System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj)
at System.Data.SqlClient.SqlDataReader.ConsumeMetaData()
at System.Data.SqlClient.SqlDataReader.get_MetaData()
at System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString)
at System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async)
at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, DbAsyncResult result)
at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method)
at System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior, String method)
at System.Data.SqlClient.SqlCommand.ExecuteDbDataReader(CommandBehavior behavior)
at System.Data.Common.DbCommand.System.Data.IDbCommand.ExecuteReader(CommandBehavior behavior)
at System.Data.Common.DbDataAdapter.FillInternal(DataSet dataset, DataTable[] datatables, Int32 startRecord, Int32 maxRecords, String srcTable, IDbCommand command, CommandBehavior behavior)
at System.Data.Common.DbDataAdapter.Fill(DataSet dataSet, Int32 startRecord, Int32 maxRecords, String srcTable, IDbCommand command, CommandBehavior behavior)
at System.Data.Common.DbDataAdapter.Fill(DataSet dataSet)
at CMS.DataProviderSQL.DataConnection.ExecuteQuery(String queryText, QueryDataParameters queryParams, QueryTypeEnum queryType, Boolean requiresTransaction)

I've checked that my permissions on SQL server are adequate. I'm not sure why it won't create the table.