yes I agreed It happens I have read some where this is kown issue and here is expalination and dolution

Dataloader runs on Java, and the issue occurs when the JVM runs out of the memory allocated to it when executed.

There are two solutions for this problem:

1. Use Data Loader version 20.0. You can download it from this link : http://www.cloudsuccess.com/resource-centre/apex-data-loader-archive/ 

2. Increase the java heap size for the Data Loader startup command (preferred method). Examples below assume that Data Loader is installed in the default location. If Data Loader is installed in a different folder, then the startup command below will look differently.

a)  If you have Data Loader shortcut on the Desktop, right-click the shortcut, select properties from the menu that opens, and in the target field modify it to look like this: 

"C:\Program Files (x86)\salesforce.com\Data Loader\Java\bin\javaw.exe" -Xms1024m -Xmx1256m -Dappdata.dir="C:\Users\<user>\AppData\Roaming" -jar "C:\Program Files (x86)\salesforce.com\Data Loader\dataloader-26.0.0-uber.jar" 

where <user> is the username of the User of the machine. 
 
b) If you do not have Data Loader shortcut on the Desktop, then click on Start Button>All Programs>salesforce.com>Data Loader and right click on the Data Loader icon there, select Properties from the popup menu that opens, and follow the steps described under a).

It might be required to go through several iterations of the steps above to find the right heap size. When setting the heap size the total amount of memory present on the system must be taken into account. Also if the system run 32 bit OS, then the heap size cannot be bigger than 2 GB. Please refer to the Java documentation for more details