In version 3, if the page is not found the macro halts. Macro Express Pro includes error handling to take care of these situations.
You may be able to use the Get Pixel Color command to do what you need in Macro Express 3. You will need to determine a fixed position on the screen that changes colors after the page has loaded.
Here's a sample of how this portion of the macro would look.
Variable Set Integer %N1% to 0
Variable Set Integer %N3% to 0
Repeat Until %N1% = 1
Get Pixel: Screen Coords: 100,100 into %N2%
Wait Time Delay 1 Seconds
If Variable %N2% = 186023
**** steps you would take after the web page is opened.
Variable Set Integer %N1% to 1
End If
Variable Modify Integer: Inc (%N3%)
If Variable %N3% = 60
Repeat Exit
End If
Repeat End
Use the Mouse Locator in the Get Pixel command to find the coordinates and the color value of the pixel to check. Use the If Variable command to see if the color value matches. If it does, then the macro performs the steps it is supposed to take on the web page and then exits out of the Repeat loop because N1 is set to 1. If it doesn't, then the macro repeats the loop again, looking for the change.
As in the example above, you might want to add a Wait Time Delay to check every so many seconds, rather than constantly checking. Use the Wait Time Delay rather than a standard Delay. This will free up CPU cycles during the wait time.
The macro has a 2nd If statement. It is incrementing the value of N3 each time through the repeat loop. Since the example has a 1 second delay, the macro would exit out of the loop approximately 60 seconds after trying to find the web page.