Avast is popular anti-virus software available for free on the Internet. Many people do use it, but on May 7, 2013 a change was made that caused software components produced by Chilkat to be flagged/removed from Avast protected system. Avast software reports that these Chilkat components contain a trojan horse virus. Chilkat maintains that their software is clean and Avast is giving a false positive when it reports it is not.
PartyCAD uses a number of Chilkat components, and Avast may remove one or more of these as a way of protecting your system. Specifically, Avast believes that the Chilkat FTP2 component contains a trojan and so removes it. This makes PartyCAD unusable. Chilkat maintains that its FTP2 component is not infected. The version of Chilkat FTP2 used in PartyCAD has not changed in 2 years, and I doubt very much that it contains a virus. No other anti-virus software is reporting this problem, and so I think this is an Avast problem.
Update: I believe Avast has remedied the problem, but if the bug got you, you will have to reinstall PartyCAD to get it working again.
If you are interested in learning more, see the links below:
Avast is at: www.avast.com
Chilkat is at: www.chilkatsoft.com