Adding DATETIME() and Status column with xp_FileExist result
You need to add code to your question that doesn't work (that causes the error you are seeing).

Having said that, you probably want to modify the code you are using to something like:

DECLARE @path varchar (100);
DECLARE @file varchar (100);
SET @file = 'C:\temp\*.*';
SET @path = 'dir /B ' + @file;

DECLARE @FILEEXISTS TABLE(
        [NAME] VARCHAR (255) NULL
);

INSERT into @FILEEXISTS 
exec master..xp_cmdshell @path ;

SELECT *
FROM @FILEEXISTS;

DECLARE @table TABLE(
        [NAME] VARCHAR (255) NULL
        , somecol VARCHAR(255) NULL
);

INSERT INTO @table(NAME)
SELECT name
FROM @FILEEXISTS;

UPDATE @table SET somecol = 'test' /* add a 'WHERE' clause if necessary */;

SELECT *
FROM @table;


This uses a table-variable to store the results, and doesn't execute the unnecessary xp_cmdshell right after the set @path=... line.

The @table declaration (and other code) I added to the end allows you grab the results into @fileexists, then insert those results into @table and add the other columns as necessary.  xp_cmdshell returns a single column of results, one line for each line output by the command it runs.