7 Common Causes Of Runtime Error 91 And How To Fix Them

Runtime Error 91 is a common issue that can pop up while working with Microsoft Office applications or any software that uses Visual Basic for Applications (VBA). This error typically occurs when you attempt to access an object that has not been set or initialized. Let's delve into the seven common causes of Runtime Error 91, how to fix them, and some helpful tips to avoid this frustrating issue.

Understanding Runtime Error 91

Runtime errors, like Error 91, are unique in that they don’t occur until the program is actually running. This makes them particularly vexing for users and programmers alike. In essence, Runtime Error 91 means that you’re trying to use an object variable that hasn’t been defined yet or has been set to Nothing.

Common Causes of Runtime Error 91

Let’s look at the seven most common causes of this error and how you can resolve them.

1. Uninitialized Object Variable

This is the most common cause of Runtime Error 91. When you declare an object variable but do not initialize it, trying to access it will throw this error.

Fix: Always ensure that you initialize your object variables. For example:

Dim myObject As Object
Set myObject = New SomeObject

2. Object Set to Nothing

If you've previously set an object variable to Nothing and attempt to use it later, you'll encounter this error.

Fix: Before accessing an object, confirm it's not set to Nothing. Use:

If Not myObject Is Nothing Then
    ' Access myObject
End If

3. Failure to Properly Load Forms

When using UserForms, if a form isn’t loaded properly, any attempt to reference it can lead to Error 91.

Fix: Make sure your forms are loaded before attempting to reference them.

If Not UserForm1.Visible Then UserForm1.Show

4. Invalid Object References

Sometimes, you may be trying to reference an object that doesn’t exist or is improperly defined.

Fix: Double-check object references to ensure they are valid and properly defined.

5. Improper Looping Constructs

When looping through collections or arrays, trying to reference an object that doesn't exist due to incorrect loop controls can lead to this runtime error.

Fix: Ensure that your loop conditions are valid and that your index variables are within bounds. For instance:

For i = 1 To UBound(myArray)
    ' Process myArray(i)
Next i

6. Incorrect Event Handling

In some cases, calling an event that hasn't been correctly set can lead to Runtime Error 91.

Fix: Verify that the events are set up correctly and confirm that your handlers are assigned properly.

7. Using Older Library References

When using external libraries that have been updated or changed, it might result in object references becoming invalid.

Fix: Check your references under Tools > References in the VBA editor and update any that are marked as “MISSING”.

Troubleshooting Runtime Error 91

If you're still facing issues even after checking the above causes, here are some troubleshooting steps you can take:

1. Step through your code: Use the debugger to step through your code and identify where the error occurs.
2. Check your variables: Verify that all your object variables are properly initialized before you use them.
3. Utilize error handling: Implement error handling to manage situations when this error does occur. For example:

   On Error Resume Next
   ' Your code here
   On Error GoTo 0
   

<div class="faq-section"> <div class="faq-container"> <h2>Frequently Asked Questions</h2> <div class="faq-item"> <div class="faq-question"> <h3>What is Runtime Error 91?</h3> <span class="faq-toggle">+</span> </div> <div class="faq-answer"> <p>Runtime Error 91 occurs when you attempt to use an object variable that has not been set or initialized.</p> </div> </div> <div class="faq-item"> <div class="faq-question"> <h3>How can I prevent Runtime Error 91?</h3> <span class="faq-toggle">+</span> </div> <div class="faq-answer"> <p>Ensure all your object variables are initialized before usage, check your references, and handle errors appropriately.</p> </div> </div> <div class="faq-item"> <div class="faq-question"> <h3>What should I do if I encounter this error?</h3> <span class="faq-toggle">+</span> </div> <div class="faq-answer"> <p>Use debugging tools to identify the line causing the error and verify that all object references are valid.</p> </div> </div> <div class="faq-item"> <div class="faq-question"> <h3>Can I fix Runtime Error 91 without programming knowledge?</h3> <span class="faq-toggle">+</span> </div> <div class="faq-answer"> <p>It may be challenging, but understanding the basics of variable initialization and object references can help.</p> </div> </div> </div> </div>

Recapping the key takeaways from our exploration of Runtime Error 91: always ensure that your object variables are initialized, check your references, and be mindful of loop structures. Error handling is also an excellent tool to have in your programming toolkit. By practicing these skills and exploring related tutorials, you can gain confidence in navigating these pesky runtime errors. So, roll up your sleeves and dive into your coding adventures, and remember that every error is a learning opportunity.

<p class="pro-note">💡Pro Tip: Always debug your code line by line to pinpoint the source of Runtime Error 91 for a quick resolution.</p>