Compiler error Message: CS0234: The namespace "system.web" does not exist in the type or namespace name "optimization" (is the assembly reference missing?)

Attribution: Song等

Today I met a problem: Compiler error message: CS0234: The namespace "system.web" does not exist in the type or namespace name "optimization" (is the assembly reference missing?).

Let me worry for a long time, how to debug and do not know where the wrong, and later asked the senior to know where the wrong.

Cause: Modify the code of a function module, afraid of affecting the function of other function module implementation, so I created a new area, to modify the module to the relevant code to copy the past, the hint with the wavy line has been modified,

This error occurs when running.

Solution: Locate the file named "Web. config" under the pre-and post-replication view folders and overwrite the contents of the "Web.config" before the copy with the "Web. config" In the content.

Note: No picture, no case, in the text may be expressed is not very clear, please understand, I try to add and case.

Compiler error Message: CS0234: The namespace "system.web" does not exist in the type or namespace name "optimization" (is the assembly reference missing?)