Under Install New Extensions enter http://connect20.magentocommerce.com/community/LinnLiveConnect
Click Install (Fig. 1.1);
3. If you're using the Magento compiler and had it enabled before installing Magento extension, go to System >Tools > Compilation and click on Run Compilation Process to re-compile Magento. Once done, enable it again by clicking on Enable;
4. Make sure WS-I Compliance is set to Yes:
System -> Configuration ->Services -> Magento Core API (Fig. 1.2);
5. Make sure PHP engine configuration has soap.so extension is installed/enabled on your server
Fig. 1.1 Fig 1.2
If you are using Magento version 1.9 or higher, it is required that the following patches are installed: SUPEE-3762, SUPEE-3941 and SUPEE-1533. Patches can be downloaded here.