If you use PayPal direct , PayPal Hosted Pro, Payflow Advanced or any centinel3dsecure enabled payment method on your site then please contact our support by sending us an e-mail to support@onestepcheckout.com and ask for special installation package that supports those payment methods (payment methods with that use 3dsecure and iframes after order is placed) . Send in your order number as well so we could validate your client status faster.

In case you run into issues after updating the package, please go through the following checklist and it should solve your issues. 

• Are template/skin/layout files from latest version really being used ? Old files may be used from theme folder.
• If you are using "Magento Admin>System>Configuration>Developer>Combine JS into same file", please disable that for checking from what theme folder the files get loaded and update files if files from old package are used
• Some cache may need to been flushed. It is best to DISABLE ALL CACHES during testing. If you are using APC/XCache/OPCache, Varnish, Redis, Cloudfare or any proxy cache, preferably disable all caches or at least check if new files are really used.
• Check One Step Checkout page source and in case there are multiple jquery imports, remove all except one. If jquery is included more than 1 time, it breaks scripts. You can ignore the One Step Checkout jquery import, it has a if-condition and only gets loaded if jquery has not been loaded before. Please see the One Step Checkout jquery import, it has an if condition and does not get loaded if jquery has already been loaded. Add this also to other jquery files and it should solve your issue.

File: skin/frontend/base/default/onestepcheckout/js/jquery-1.11.3.min.js
Code:
if (typeof jQuery === 'undefined') {
[...Jquery file content...]
}