Hi
has I see, can be some things like you textbox is enabled? if so, then see if it is readonly.
try the validation code on the valid event and don't put the KEYBOARD TAB.
If you are on the valid event, VFP automatically jumps to the next control if you return .T. on this method, i.e.

Local lnValid, cValue && or the typoe of value c=char,n=number,l=logical,etc

cValue = This.Value

If cValueIsValid && valid conditions
lnValid = .T.
Else
* Send a wait window message to indicate the mistake
lnValid = 0 && 0 avoid to go out of the control
EndIf

Return lnValid


**
I Hope this help

Mauricio