First, can I suggest you change your username as this is publicly visible? You can do this by clicking on the 'Your Profile' link above (it is next to your user name) and then selecting 'Edit Account'.
I think there are a couple of problems happening here. First, you have installed 2.5 and then tried to revert to an earlier version. Version 2.5 likely produced application data that cannot be understood v2.2.6 and this is likely the cause of the exception you are seeing.
Regarding licensing, you can install LogViewPlus on as many machines as you need, but only while the support contract is active. New installs are prohibited after support expiry. All existing installs will continue to work normally indefinitely.
You can check the status of your license key here: https://www.logviewplus.com/check_key.aspx
The LogViewPlus license tries to strike a balance between the high upfront cost required for 'own forever' software and the often frustrating SAAS 'rent never own', or machine based models. When you buy LogViewPlus you own it forever on all of your current machines. New machines will require a new license if you are out of the support period.
We also offer steep discounts on license renewals of 70% for one year or 75% for three years.
Hope that helps. Please let me know if you have any further questions or issues.