Malwarebytes downloading problems

Having only MSE on two W7 pc's and on three W8.1 pc's, I thought that it would be sensible to heed the experts on this forum and on the W7 forum and start using Malwarebytes. I installed the free version on the first four, but forgot to untick the "trial version" on no 5. When it finished loading, I uninstalled from the W8.1 pc and when I reinstalled the option for free only no longer existed. I don't want the pro version so if anyone knows how to solve this problem, I would be grateful.

After running the uninstall you can use CCleaner to clean up Registry Issues. I advise making a Restore Point and selecting to back up the Registry before selecting to resolve all issues. CCleaner is reliable but I did get one buggy version where I got burnt because I didn't select registry backup when cleaning. In the very next version that bug was fixed. Better safe than sorry though.

I'm guessing MBAM leaves a setting in the Registry so that you won't keep running Trial and getting a new 30 days or whatever it is, by uninstalling then installing again.

Perhaps if I wait for the trial period to expire I will be able to load the free version?

Just let the Pro run and expire, it will then revert to the free version.