我在ASP.NET中遇到解析器错误，如何处理它以及为什么会出现此错误？我该如何解决？
Server Error in '/' Application.
Parser Error
Description: An error occurred during the parsing of a resource required to service this request. Please review the following specific parse error details and modify your source file appropriately.
Parser Error Message: Could not load type 'BrightPublication.PurchaseOrderForm'.
Source Error: