http image upload error

hello .. I have been having this problem for weeks and tried many solutions … they are as follows
1. Tried resizing images using various methods .. use mostly optimised JPG files but have tried other kinds to see if it helps .. it doesn’t.
2. I have added code to the hcaccess file namely codes recommended for if module security, i.e. turn off sec filter etc .. (various versions are written below)
3. I have tried looking at the upload folder path to see if it is correct but cannot find this in wp 3.5.1..
4. I tried installing other flash uploaders but that didnt work ..

I do not have any problems uploading images to widgets or the header.
Occasionally the image does upload to the media library but only for a few goes than I get the http error in red again … and I cannot see why some work and some don’t …

I am a wordpress newbie and would really really appreciate simple language if you are kind enough to reply. I also am running the site in admin mode .. looking at it won’t tell you anything about the images ..

thanks for your help in advance ..

Code tried

#BEGIN Image Upload HTTP Error Fix
<IfModule mod_security.c>
<Files async-upload.php>
SecFilterEngine Off
SecFilterScanPOST Off
</Files>
</IfModule>
<IfModule security_module>
<Files async-upload.php>
SecFilterEngine Off
SecFilterScanPOST Off
</Files>
</IfModule>
<IfModule security2_module>
<Files async-upload.php>
SecFilterEngine Off
SecFilterScanPOST Off
</Files>
</IfModule>
#END Image Upload HTTP Error Fix

#BEGIN Image Upload HTTP Error Fix
<IfModule mod_security.c>
SecFilterEngine Off
SecFilterScanPOST Off
</IfModule>
<IfModule mod_security.c>
<Files async-upload.php>
SecFilterEngine Off
SecFilterScanPOST Off
</Files>
</IfModule>
#END Image Upload HTTP Error Fix 

<IfModule mod_security.c>
SecFilterEngine Off
SecFilterScanPOST Off
</IfModule>

#BEGIN Image Upload HTTP Error Fix
<IfModule mod_security.c>
SecFilterEngine Off
SecFilterScanPOST Off
</IfModule>
#END Image Upload HTTP Error Fix