For Win7 x64 users: I found the required dll (and others) in C:\Program Files (x86)\Common Files\Teleca Shared and ended up copying them all to C:\Windows\SysWOW64
For x86 (32-bit) users: copy the files to C:\Windows\System32
Once copied, the HTC Sync program opened without issue, no rebooting or reinstalling required. Good luck!