Incorrect syntax near '1'

using (conn = new SqlConnection(GeminiConnString))
{
using (command = new SqlCommand("dbo.CZ_InsertIntoProjectManagementOutstandingExcel", conn))
{
        conn.Open();
        command.CommandType = CommandType.StoredProcedure;
        command.Parameters.AddWithValue("@startDate", StartDate);
        command.Parameters.AddWithValue("@endDate", EndDate);

        command.ExecuteNonQuery(); //<-- error here

    //Sto-Pro Details
    SqlDataAdapter da = new SqlDataAdapter(command);
    DataSet ds = new DataSet();
    da.Fill(ds);
    dt = ds.Tables[0];

    conn.Close();
}
}

ALTER PROCEDURE [dbo].[CZ_InsertIntoProjectManagementOutstandingExcel]
-- Add the parameters for the stored procedure here
@STARTDATE VARCHAR(MAX),
@ENDDATE VARCHAR(MAX)
	
AS
BEGIN
-- SET NOCOUNT ON added to prevent extra result sets from
-- interfering with SELECT statements.
SET NOCOUNT ON;

DECLARE @SQL NVARCHAR(MAX)

SET @SQL = 
'
DROP TABLE CustomizationYesNo
DROP TABLE SystemDetermination
DROP TABLE ProjectName
DROP TABLE CustName
DROP TABLE RequesterName
DROP TABLE VersionNumber
DROP TABLE GetTargetDate
DROP TABLE GetActualDate
DROP TABLE ProjectManagement

CREATE TABLE CustomizationYesNo(IssueID VARCHAR(100), YesNo VARCHAR(100))
INSERT [CustomizationYesNo]
SELECT issueid, CASE WHEN projectcode IN (''CESS'', ''CHRM'') THEN ''Yes'' ELSE ''No'' END as Customization 
FROM [dbo].[gemini_issuesview]

CREATE TABLE SystemDetermination(IssueID VARCHAR(100), Systems VARCHAR(100))
INSERT [SystemDetermination]
SELECT
i.issueid, 
CASE SUBSTRING(projectname, 1, 1) 
WHEN ''E'' THEN ''ESS''
WHEN ''F'' THEN ''HRMS''
ELSE ''PayFlex'' 
END AS System 
FROM [dbo].[gemini_projects] p, [dbo].[gemini_issuesview] i
WHERE p.projectid = i.projectid

CREATE TABLE ProjectName(IssueID VARCHAR(100), ProjectName VARCHAR(100))
INSERT [ProjectName]
SELECT i.issueid, projectname 
FROM [dbo].[gemini_projects] p,[dbo].[gemini_issuesview] i
WHERE p.projectid = i.projectid 

CREATE TABLE CustName(IssueID VARCHAR(100), CustomerName VARCHAR(100))
INSERT [CustName]
SELECT i.issueid, fielddata 
FROM [dbo].[gemini_customfielddata] c, [dbo].[gemini_issuesview] i 
WHERE customfieldid = 200 AND c.issueid = i.issueid 

CREATE TABLE RequesterName(IssueID VARCHAR(100), ReqName VARCHAR(100))
INSERT [RequesterName]
SELECT i.issueid, firstname 
FROM [dbo].[gemini_users] u , [dbo].[gemini_issuesview] i 
WHERE u.userid = i.reportedby

CREATE TABLE VersionNumber(IssueID VARCHAR(100), VersionsNum VARCHAR(100))
INSERT [VersionNumber]
SELECT  i.issueid, MAX(v.versionnumber) AS Versions
FROM [dbo].[gemini_versions] v, [dbo].[gemini_issuesview] i
WHERE i.projectid = V.projectid
GROUP BY i.issueid
ORDER BY i.issueid

CREATE TABLE GetTargetDate(IssueID VARCHAR(100), TargetDate VARCHAR(100))
INSERT [GetTargetDate]
SELECT  issueid, fielddata 
FROM [dbo].[gemini_customfielddata]
WHERE customfieldid = 215

CREATE TABLE GetActualDate(IssueID VARCHAR(100), ActualDate VARCHAR(100))
INSERT [GetActualDate]
SELECT issueid, fielddata 
FROM [dbo].[gemini_customfielddata]
WHERE customfieldid = 217



CREATE TABLE ProjectManagement(Category VARCHAR(100), Systems VARCHAR(100), Module VARCHAR(100), Customization VARCHAR(100), Descriptions VARCHAR(MAX),
Customer VARCHAR(100), Statuss VARCHAR(100), CSD_Requester VARCHAR(100), CSD_Request_Date VARCHAR(100), GeminiID VARCHAR(100), Versions VARCHAR(100),
TargetDate VARCHAR(100), ActualDate VARCHAR(100))
INSERT [ProjectManagement]
SELECT i.typedesc, s.Systems, p.ProjectName, c.YesNo, i.longdesc, n.CustomerName, i.statusdesc, r.ReqName, REPLACE(CONVERT(VARCHAR(100), i.created, 106), '' '', ''-''), i.issuekey, v.VersionsNum, REPLACE(t.TargetDate, ''/'', ''-''), REPLACE(a.ActualDate, ''/'', ''-'') 
FROM [dbo].[gemini_issuesview] i, SystemDetermination s, ProjectName p, CustomizationYesNo c, CustName n, RequesterName r, VersionNumber v, GetTargetDate t, GetActualDate a
WHERE i.issueid = s.IssueID AND i.issueid = p.IssueID AND s.IssueID = p.IssueID
AND i.issueid = c.IssueID AND p.IssueID = c.IssueID AND s.IssueID = c.IssueID
AND i.issueid = n.IssueID AND p.IssueID = n.IssueID AND c.IssueID = n.IssueID AND s.IssueID = n.IssueID
AND i.issueid = r.IssueID AND p.IssueID = r.IssueID AND c.IssueID = r.IssueID AND n.IssueID = r.IssueID AND s.IssueID = r.IssueID
AND i.issueid = v.IssueID AND p.IssueID = v.IssueID AND c.IssueID = v.IssueID AND n.IssueID = v.IssueID AND s.IssueID = v.IssueID AND r.IssueID = v.IssueID
AND i.issueid = t.IssueID AND p.IssueID = t.IssueID AND c.IssueID = t.IssueID AND n.IssueID = t.IssueID AND s.IssueID = t.IssueID AND r.IssueID = t.IssueID AND v.IssueID = t.IssueID
AND i.issueid = a.IssueID AND p.IssueID = a.IssueID AND c.IssueID = a.IssueID AND n.IssueID = a.IssueID AND s.IssueID = a.IssueID AND r.IssueID = a.IssueID AND v.IssueID = a.IssueID AND t.IssueID = a.IssueID   

SELECT  * FROM ProjectManagement	   		
	'
	
IF(@STARTDATE != '' AND @ENDDATE != '')
	SELECT @SQL = @SQL + ' WHERE CONVERT(DATE, CSD_Request_Date) BETWEEN CONVERT(DATE, '+@STARTDATE+') AND CONVERT(DATE, '+@ENDDATE+')'
ELSE
	SELECT @SQL = @SQL

SELECT @SQL = @SQL
EXEC sp_executesql @SQL 
   
END