I am getting error while uploading from any pages. Folders are exists, file permissions are set to 755 but still getting error.

What error exactly? What is your code?

Code

if(isset($_POST['upload_attachemt']))
{
    $path = "uploaded_attachments/"; // Upload directory
    if($_FILES['attachment_file']['name']!='')
    {
        $attachment_file = md5(uniqid(rand(), true)).'.'.file_ext($_FILES['attachment_file']['name']);
        move_uploaded_file($_FILES["attachment_file"]["tmp_name"], $path.$attachment_file);
    }
    if(mysql_query("insert into tbl_attachment set attachment_name='".$_POST['attachment_name']."', attachment_userid=".$_REQUEST['user_id'].", attachment_file = '".$attachment_file."', attachment_date = '".date('Y-m-d H:i:s')."' "))
        header("Location:".$_SERVER['PHP_SELF']."?msg=Uploaded Successfully !!&user_id=".$_REQUEST['user_id']."&action=".$_REQUEST['action']);
}   

Design

if($_REQUEST['action']=='attachment')
{
   ?>
    <style>label{ font-weight:bold;}</style>
    <fieldset style="font:normal 12px Verdana; margin-top:20px;">
        <form method="post">
        <table style="font:normal 12px Verdana; width:100%" cellpadding="0" cellspacing="0">
        <tr>
            <td width="25%" style="background-color:#999999; font-weight:bold;padding:2px;">Attachment Name</td>
            <td width="50%" style="background-color:#999999; font-weight:bold;padding:2px;">View Attachment</td>
            <td width="25%" style="background-color:#999999; font-weight:bold;padding:2px;">Attachment Date</td>
        </tr>
        <?php
        $userdetail=mysql_query("select * from tbl_attachment where attachment_userid=".$_REQUEST['user_id']." order by attachment_date desc");
        while($row=mysql_fetch_array($userdetail))
        {
        ?>      
            <tr>
                <td style="padding:2px; border:1px #999999 dotted">
                <input type="checkbox" name="attachments[]" value="<?php echo $row['attachment_id']; ?>"  />
                <?php echo $row['attachment_name']; ?></td>
                <td style="padding:2px; border:1px #999999 dotted"><a href="uploaded_attachments/<?php echo $row['attachment_file']; ?>"><?php echo $row['attachment_file']; ?></a></td>
                <td style="padding:2px; vertical-align:top; border:1px #999999 dotted"><?php echo date('d-M, Y h:i:s A', strtotime($row['attachment_date'])); ?></td>

            </tr>
        <?php
        }
        ?>  
        <tr>
            <td width="25%" style="background-color:#999999; font-weight:bold;padding:2px;"></td>
            <td width="50%" style="background-color:#999999; font-weight:bold;padding:2px;"></td>
            <td width="25%" style="background-color:#999999; font-weight:bold;padding:2px; text-align:right">
            <input type="submit" name="delete_attachments" value="Delete"  />
            </td>
        </tr>
        </table>
        </form>
    </fieldset>

        <fieldset style="font:normal 12px Verdana; margin-top:20px;">
        <form method="post" enctype="multipart/form-data">
        <table style="font:normal 12px Verdana; width:100%" cellpadding="0" cellspacing="0">
        <tr>
            <td width="31%" style="background-color:#999999; font-weight:bold;padding:3px 5px;">Upload Attachment</td>
        </tr>
        <tr>

            <td width="31%" style="background-color:#999999; font-weight:bold;padding:2px;">
            <input type="text" name="attachment_name" id="attachment_name" required style="width:100%;" placeholder="Attachment Name ..." />
            </td>
        </tr>

        <tr>
            <td width="31%" style="background-color:#999999; font-weight:bold;padding:2px;">
            <input type="file" name="attachment_file" id="attachment_file" required style="width:100%;" placeholder="Attachment Name ..." />
            </td>
        </tr>        
        </table>
        <input  type="submit" name="upload_attachemt" value="Upload" id="upload_attachemt" style="margin-top:5px; float:right;"  />
        </form>

    </fieldset>
    <?php
}       

Says permission denied, so your permissions are not set correctly.

It already set permission to 777

Are you sure the permission are on the correct folder? Most of the time the error messages are correct.