Helping people with computers... one answer at a time.
mwsbar.dll is a toolbar for Internet Explorer commonly part of "My Web Search". Getting rid of mwsbar.dll, or references to it, isn't terribly difficult.
I have a Rundll error message that states: Error loading C:\Progra~1\MYWEBS~1\Bar\1.Bin\MWSBAR.dll. How can I fix that?
There's a lot left unsaid in your question - like what system you're running on, what browser you use, and even when the error is happening.
But, I'm going to make a few assumptions, and follow those up with a wild guess.
Maybe it'll help.
First, "mwsbar.dll" is associated with the "My Web Search" toolbar which is downloaded and installed with several different free products. The first step is simple: go to Control Panel, Add or Remove Programs... and look for and uninstall "My Web Search Bar". It can actually be present under several different names, so look for any of the other items listed here.
Even though My Web Search is not spyware, it's apparently flagged by some anti-spyware utilities. So my next recommendation is, of course, to make sure you're running a good, up-to-date spyware scan.
Now, all of that probably assumes that things are working - and obviously, since you're getting an error message, something isn't quite right. Those steps may, or may not, clear up the problem. Our next step is to address the symptom.
mwsbar.dll is what's called a "browser helper object" or BHO. It's something that's installed into Internet Explorer. I have to assume that that's what you are using, and that the error appears when you start IE.
Fortunately, IE has an often over-looked interface for dealing with "Browser Helper Objects".
In Internet Explorer, click on the Tools menu, and then click on the Manage Add-Ons... menu item. You should get a dialog box similar to this:
The list of items therein will probably be quite different for you.
Now, you may already see something listed with the "My Web Search" name. But if not, grab the scroll bar at the bottom of the list and drag it to the right. The list will scroll to the left, and display an additional column - the name of the File that provides the BHO:
Here you'll most likely see "mwsbar.dll" listed one or more times. (You may need to scroll down through the entire list.)
Once you find it, click on it, then click on the Disable Setting below the list. Close the Add-on manager, close IE, and see if that didn't solve your problem.
If it didn't (and you're sure that all instances of mwsbar.dll are removed from the Add-on manager), then the next step is to remove it manually. Rather than repeat someone else's work, I'll simply point you here: Fun Web Products "My Web Search" Removal Instructions and Help, which includes instructions to use the diagnostic tool HijackThis to remove the registry entries that relate to My Web Search.