My first thoughts are:
1. There was a problem with Kaspersky AV deleting the Ad-aware mia.lib file, but it's been resolved. If you have Kaspersky, make sure you have updated definitions before attempting a reinstall.
2. the dowloaded installer file is corrupt.
Try downloading again from
here. To prevent problems, do a
clean uninstall first. You can do this yourself if you're experienced with finding/deleting folders, files, and registry entries; or you can use programs like these
useful free tools. WICU cleans up botched installs and Revo Uninstaller on the highest setting will remove all traces of Lavasoft/Ad-Aware before you reinstall. Also, I find it best to stop all running processes before installing any software.
3. a malware infection is preventing installation.
If you suspect your system is infected, read the instructions in my signature about posting a log in the HijackThis forum. Copy/paste or link to this thread to describe the problem, and somebody there can help you with malware removal.