The ‘Live Semantic Error feature’ in Visual Studio 2008 SP1 and onwards indicates problems in your code immediately as it detects one, without the need for a compile. Red squiggly or wavy lines appear beneath your code that is incorrect or could cause a problem. For example, there is not method called Closing() in the SerialPort class. So as soon as you type it, a red squiggly line appears indicating it is a syntax error.
Now this could be a time saver in many scenarios, but could also be distracting at times. If you want to temporarily turn it off, here’s how to do so.
Open Visual Studio 2008/2010 > Go to Tools > Options > Text Editor > C# > Advanced > and uncheck the ‘Show live semantic errors’ check box as shown below
Now the squiggles will not appear as you type.
Note: When you compile your code and there are semantic errors detected by the compiler, blue squiggles appear beneath the code that is causing the error.