Symptoms
When trying to start MT4, you receive a message that says "Unable to load TDS library".
Cause
This is typically caused by antivirus software that fails to consider the digital signature of files and issues a false positive on the tdslib.dll file installed by the Tick Data Suite. This has been mostly noticed in the presence of Norton Antivirus which also fails to notify the user about the actions it has taken.
Resolution
First of all, you need to check if the file tdslib.dll is present in C:\Program Files (x86)\eareview.net\Tick Data Suite\ (or for x86 Windows installations C:\Program Files\eareview.net\Tick Data Suite\).
If the file is there, your antivirus is probably blocking access to it and you will have to whitelist the file. Please refer to the manual of your antivirus for instructions on how to do that or just run a quick Google search.
If the file is not there, you should open Control Panel, head to Programs (alternatively Add/Remove Programs or Programs and Features depending on your Windows version), select the Tick Data Suite entry, click the Uninstall/Change button and when prompted select Repair. It's important to note that your antivirus might flag the file once more so you should either whitelist the file or disable the antivirus during the install process.
If you're in doubt about the authenticity of the file, you can verify its digital signature by going to the Digital Signatures tab in the File Properties dialog, selecting one of the digital signatures and clicking the Details button. You can also submit the file for further verification with multiple antivirus engines at virustotal.com.