Here are two common ways to implement error handling for conditional formatting formulas in Excel:

1. Using the IFERROR Function:

The IFERROR function allows you to specify what to display in a cell if the formula within it encounters an error. You can leverage this function within your conditional formatting rule.

Here's how it works:

* Conditional Formatting Setup: Follow the usual steps to set up a new conditional formatting rule. In the "Format values where this formula is true" section, enter the following formula:

```excel
=IFERROR(Your_Original_Formula, "Error message/formatting")
```

* Replace the placeholders:
- `Your_Original_Formula`: This is your actual conditional formatting formula that might generate errors.
- `"Error message/formatting"`: Replace this with the text you want to display or the formatting you want to apply if an error occurs (e.g., a specific cell color).

Example:

Let's say you want to highlight cells with values greater than 10 but display "Data Entry Error" if the cell contains an error.

Your formula would be:

```excel
=IFERROR(A1>10, "Data Entry Error")
```

2. Using Nested IF Statements:

Another approach is to use nested IF statements to check for specific errors before applying your conditional formatting.

Here's a basic example:

```excel
=IF(ISERROR(A1), "", IF(A1>10, "Highlight", ""))
```

* This formula first checks if there's an error in cell A1 using ISERROR. If there is, it displays nothing ("").
* If there's no error, it then checks if the value in A1 is greater than 10. If it is, it displays "Highlight" (you can replace this with your desired formatting).
* If neither condition is met, it displays nothing, leaving the cell unformatted.

Choosing the Right Method:

* IFERROR: This is a simpler approach if you just want to display a generic message or formatting for any error.
* Nested IFs: This method offers more control if you want to handle specific errors differently (e.g., display different messages for #NA, #VALUE, etc.).

Remember to adjust the formulas and formatting based on your specific conditional formatting needs and desired error handling behavior.