Can "SendKeys" be blocked by an Application?

[David_G]

Hi Excellers,

I have been working on an Excel VBA project today (at work) and I
tried to send keys to a Windows application (a non-Office app) but
they appeared to have no effect. As suggested by the help file I
wasn't stepping through the code, instead I ran it from the Excel
Interface -> "Run Macro". I tried the Calculator example in the
SendKeys help file and it worked perfectly. This leads me to think
that somehow this SendKeys Statement is being blocked by the other
application. Is this what is happening? Is it possible to block
sendkeys?
Much appreciated
David_G