Starting with 2010 SP3.0, SolidWorks is checking whether you are on subscription before you install the service pack.  With SP3.0 you will just get a warning if you are not on subscription but starting with SP4.0 you will not be able to install. 

For network licenses, the expiration date is saved on the license server and that is the date that is checked during installation.  Depending on the date the SNL Manager was activated and the subscription expiration date, you may get the message that your subscription has expired even though it has been renewed.

Example: 2010 was installed and activated 11/20/2009.  The subscription expiration date at that time was 12/31/2009.  Since then you have renewed your subscription and the new expiration date is 12/31/2010.  On April 28, 2010, you install SP3.0.  During installation, the server is checked and comes back with an expiration date of 12/31/2009 (the expiration date when the license was activated) so you get a message that you are not on subscription.

The fix is very simple – just run the SNL Manager on the server, click the Modify button, and select Activate/Reactivate license.  The expiration date will be updated on the server and you should not have any problems installing future service packs.

If you have any questions about this, please call Support at 763-560-8600, option 4, and we will be glad to help.