if you are running into these problems repeatedly there is obviously something else going on. With out some more details, it is hard to tell why you keep having this problem. here are some things to double check that may contribute to running into these issues:
1) before installing, save the .mxp file to your computer. When you click the link in the download center, you may be prompted to either open the file or save it, make sure to select the option to save it.
2) Instead of double clicking the MXP file to begin the installation, start the installation manually. In Dreamweaver, go to Commands -> Manage Extensions to open the extension manager. Once the extesnion manager is open, close Dreamweaver before proceeding. In the Extension Manager, click the install extesnion icon. Browse to the location where you saved the MXP file and select it to begin the installation.
3) If you are planning to install an updated version of an extension, first Uninstall the previous version from the extesnion manager.
4) When using the extesnion manager, always make sure Dreamweaver is closed.
5) Sometimes Anti Virus software, or other software that performs real time scanning on the file system can cause conflicts. Turn off your anti virus software before installing.
6) If you are on a Windows computer, make sure you are not installing while logged in using the Windows Administrator account, you should create a secondary user account, you can grant that account administrator privileges.
We have some youtube videos at the following URL:
that walk through the proper steps for installing and updating WebAssist Extensions.