I found a solution to this problem by accident. I am using ACT! 16 on Windows 8.1
I had a problem with another program which when closing gave this message "Unable to create file ............. Access Denied"
The answer to this problem was the Roaming Folder in User\Update\ was read only. After clearing this setting that program closed properly.
I had been unable to open ACT, (had been working for about a week then changed, perhaps due to change of anti-virus software?) After looking on this forum and the knowledgebase I found that the problem could be overcome by deleting about half the entries in the Plugins folder. After the Roaming folder was reset I copied back all the entries to the Plugins folder and ACT now opens properly.
Interestingly enough the folder seems to have reverted to read only.