Block users from entering specific data

[Watchdawg]

This is probably easy for you folks. I have a tab, "Request Form" where the customer will place the material they're requesting along with quantity and unit of measure (B3, C3, D3). The first tab, "Items Not To Move" has a list of materials that they are not permitted to request. So here's my dilemma...
If the customer enters a value into B3 (Requested Material) on the Request Form tab that is found in the "Items Not To Move" tab, A1:A120, I need it to issue a pop-up message informing them that the material is blocked for transfer, and then keep them from entering any data in C3 or D3 (or delete the data from the entire row).

Pipe Dream?

 

[Scott T]

Select B3 on your request form
Select Data validation from the Data tab in the ribbon
in Allow: select Custom
in Formula use. Adjust the range $A$2:$A$99 so it has the list of items you do not what to be entered.

=COUNTIF('Items Not To Move'!$A$2:$A$99,B3)=0

 

[Watchdawg]

Absolutely perfect! Thank you!
No, a message box pops up that states "The value you entered is not valid. A user has restrivted values that can be entered into this cell". Is there any way to alter the message so that I can add something more descriptive to give them instructions on how to proceed if they have a special circumstance? I'm assuming this would include VB code?

 

[Scott T]

Select B3 and go back into data Validation.
You will see the validation you just setup
click on the Error Alert tab and you can enter a custom message.