It can be quite complicated to get a Schengen visa, especially if you do not know much about it and there is no specialist to assist you; but even when you already get your Schengen visa, you still might have some questions.
Many Schengen visa applicants are not sure what the visa validity and period of stay are.For instance, one gets mistaken for the other quite often, although they are two different items. Your Schengen visa may be valid from 25 June 2011 until 25 June 2012 - one year validity, - but it doesn't mean that you may remain in the Schengen area for 365 days - you visa always clarifies that and normally gives you the right to stay in a Schengen country for either 90 or 180 days. Here is a real life situation to demonstrate this: one of our customers has a one year French Schengen visa valid until February 20, 2011.
The customer assumed that his French Schengen visa would be automatically cancelled and he bought a holiday in Spain starting on February 22, 2011. Of course, ther is not enough time for applying for the Spanish Schengen visa because they will not process the visa application within 2 days. What does he need to do to make this trip happen? The first thing to do is to cancel his French visa, since the rule is that an applicant cannot hold two valid Schengen visas in the passport. The cancellation stamp makes the current Schengen visa invalid and one may apply for a new visa for any Schengen country.
Don't worry, the cancellation stamp we are talking about is not the one you should try to avoid - the cancellation stamp will not be a problem next time you apply for a Schengen visa, it only shows the visa officer that you may apply for a new visa. This stamp is put on your visa and reads “Cancelled without prejudice”.
What you need to remember is that it is a mistake to think that a valid French Schengen visa can be cancelled by the Spanish consulate, and vice versa. If you have to cancel your existing Schengen visa, you must go to the consulate which issued that visa.