Bahadir,
ErrorProvider is a non-visual .NET component, and it is not shown in the Object Browser tree. TestComplete has access to internal objects, methods and properties of .NET applications. So, you can get the error text by these methods and properties. ErrorProvider contains the GetError method that returns the error text set for a control.
Below, is a VBScript code snippet that demonstrates how you can call this method from script:
Sub Test
' Obtain your form
Set frm = Sys.Process("WindowsFormsApplication1").WinFormsObject("Form1")
' Obtain the control, for which you would like to obtain the error text
Set control = frm.textBox1
' You can also use this code
' Set control = frm.WinFormsObject("textBox1")
' Obtain the ErrorProvider component that is on the form.
' ErrorProvider is a non-visual component, so I get it through the form's native property.
Set errorProviderObj = frm.errorProvider1
' Obtain the error text for the needed control.
s = errorProviderObj.GetError(control)
' Log result
Log.Message s
' Voila! :-)
End Sub
I'd like to note that the application can set the error text for a control right before the ErrorProvider starts blinking. If this is what you have in your application, call this script routine after ErrorProvider starts blinking.