Strang Query Timeout Error

I have created a stored procedure which searches one or more requests (request is a table) according to the given parameters and returns Rows from Request table. I have used Full Text Search function i.e. Contains() in this Query. I have problem with Full Text search, when user first time executes query with Contains() function it works fine and continues working fine for 10 to 15 times or more executions. But after some searches the system starts saying Timeout Error. The very strange situation is that the application is developed in Visual Basic and if we run stored procedure through Visual Basic it says Time Out but at the same time when we run the same stored procedure with same parameters from SQL Server Management Studio, it runs immediately and takes no time in execution. Also I have tested the Stored procedure without the Contains function and in this case it works fine. It only hangs when we search for more than 10 or 15 times.


Does anyone know what is the problem here?, i am posting here my code too,




Code Snippet
-- =============================================
-- Author: Arsalan Tamiz
-- Create date: 17-Mar-2007
-- Description: Request Search Engine
-- =============================================
ALTER PROCEDURE [RVO].[LookUpRequest]

-- Add the parameters for the stored procedure here
@Account_ID int = NULL,
@Comp_Name varchar(255) = NULL,
@RVO_ID varchar(100) = NULL,
@RVO_CreateDateStart datetime = NULL,
@RVO_CreateDateEnd datetime = NULL,
@RVO_LockStatus int = NULL, -- NULL = All, 0 = Not Locked / Open, 1 = Locked
@RVO_FinalizeStatus int = NULL, -- NULL = All, 0 = Not Finalized, 1 = Finalized
@SEStatus int = NULL, -- NULL = NOT use, 0 = NOT set, 1 = SET to any
@SE_ID varchar(100) = NULL, -- SE ID
@RVO_CommitStatus int = NULL, -- NULL = All, 0 = Not Commit, 1 = Committed
@RVO_Voided int = NULL, -- NULL = All, 0 = Not Voided, 1 = Voided
@Area_IDNotSet bit = NULL,
@NH_IDNotSet bit = NULL,
@LandmarkNotSet bit = NULL,
@ClassNotSet bit = NULL,
@City_ID int = NULL,
@Area_ID int = NULL,
@NH_ID int = NULL,
@Keyword varchar(255) = NULL,
@Brand varchar(255) = NULL,
@CompType_ID int = NULL
AS
BEGIN

-- SET NOCOUNT ON added to prevent extra result sets from
-- interfering with SELECT statements.
SET NOCOUNT ON;

DECLARE @kc varchar(255);

If @Keyword IS NULL

SET @kc = @Keyword;
Else

SET @kc = Gen.GetContainsCriteriaGen(@Keyword);


SELECT *
FROM RVO.tbl_RequestRVO
WHERE

(@CompType_ID IS NULL OR CompType_ID = @CompType_ID) AND
(

@kc IS NULL OR

Contains(RVO_Keywords, @kc)
) AND
(

@Brand IS NULL OR

Exists(

SELECT * FROM RVO.tbl_RequestRVOBrand


WHERE Brand_Name LIKE @Brand + '%' AND Request_ID = RVO.tbl_RequestRVO.Request_ID
)
) AND
(

(
@City_ID IS NULL AND
@Area_ID IS NULL AND
@NH_ID IS NULL AND
@Area_IDNotSet IS NULL AND
@NH_IDNotSet IS NULL
) OR
Exists(


SELECT * FROM RVO.tbl_RequestRVOAddress


WHERE (


@Area_IDNotSet IS NULL OR
(@Area_IDNotSet = 1 AND Area_ID IS NULL)
) AND

(

@NH_IDNotSet IS NULL OR
(@NH_IDNotSet = 1 AND NH_ID IS NULL)
) AND
(@City_ID IS NULL OR City_ID = @City_ID) AND
(@Area_ID IS NULL OR Area_ID = @Area_ID) AND
(@NH_ID IS NULL OR NH_ID = @NH_ID) AND
Request_ID = RVO.tbl_RequestRVO.Request_ID AND
Address_Voided = 0
)
) AND
(

@LandmarkNotSet IS NULL
OR
NOT Exists (


SELECT TOP 1 *
FROM RVO.tbl_RequestRVOAddressLandmark

INNER JOIN RVO.tbl_RequestRVOAddress ON RVO.tbl_RequestRVOAddressLandmark.RequestAddress_ID = RVO.tbl_RequestRVOAddress.RequestAddress_ID
WHERE Request_ID = RVO.tbl_RequestRVO.Request_ID AND

Address_Voided = 0
)
) AND
(

@ClassNotSet IS NULL
OR
NOT Exists (


SELECT TOP 1 *
FROM RVO.tbl_RequestRVOClass
WHERE Request_ID = RVO.tbl_RequestRVO.Request_ID
)
) AND
(Account_ID = @Account_ID OR @Account_ID IS NULL) AND
(@Comp_Name IS NULL OR RVO_CompName LIKE @Comp_Name) AND
(@RVO_ID IS NULL OR RVO_ID = @RVO_ID) AND
(RVO_CreateDate >= @RVO_CreateDateStart OR @RVO_CreateDateStart IS NULL) AND
(RVO_CreateDate <= @RVO_CreateDateEnd OR @RVO_CreateDateEnd IS NULL) AND
(

@RVO_LockStatus IS NULL OR
(RVO_LockDate IS NULL AND @RVO_LockStatus = 0) OR
(RVO_LockDate IS NOT NULL AND @RVO_LockStatus = 1)
) AND
(

@RVO_FinalizeStatus IS NULL OR
(MO_FinalizeDate IS NULL AND @RVO_FinalizeStatus = 0) OR
(MO_FinalizeDate IS NOT NULL AND @RVO_FinalizeStatus = 1)
) AND
(

@RVO_CommitStatus IS NULL OR
(Comp_ID IS NULL AND @RVO_CommitStatus = 0) OR
(Comp_ID IS NOT NULL AND @RVO_CommitStatus = 1)
) AND
(

( -- if SE = SET Then SE_ID must NOT be NULL

@SEStatus = 1 AND
(

(SE_ID IS NOT NULL AND @SE_ID IS NULL) OR
(SE_ID = @SE_ID)
)
) OR
(@SEStatus = 0 AND SE_ID IS NULL) OR
@SEStatus IS NULL
) AND
(RVO_Voided = @RVO_Voided OR @RVO_Voided IS NULL)
ORDER BY

Account_ID, RVO_CreateDate;



END