Macro hangs if too many records

[KCarpenter]

A large macro that validates information on a 40 column sheet works fine if I check a certain number of rows. When it checks over 10000, the userform reports and "Excel not responding" message and it hangs. Sometimes it finishes eventually, but starting it again generates various errors that some variables are not defined or other phantom problems. Closing and opening Excel fixes it, but I'm still limited to the number of records I can check. Is this a memory issue? Is there a fix?
KCarpenter