hello Vidswar,
there's couple of probabilities here! it could be a validation in a rule, it could be a data validation error, for example, you have a date field where it has a text typed in it.
First thing first, usually when you get this error in a infopath form, the field or data with error will be colored in red for you to notice and change it! try to modify the existing form again and fetch your form for a red-labeled data (it could be the
people picker).
i would first ask you to make sure you're using the people picker correctly! (i assume you could miss-use it), in people picker, there's 3 ways you can fill in, (1)typing the account name for the user (for Aabed Yassine for example it could be Ayassine),
(2) typing the user name (Aabed Yassine), (3) if you dont know whats the exact user name or their account, click on the book icon in the people picker, where you can browse and search for users.
NOTE: user name/ account/ email in people picker should be udnerlined automatically if the username/ account/ email you specified is VALID, make sure to check this!
if you're sure you're filling the people picker with a valid data:
-Run through your form rules, get to know what rules you have, what they do and when.
-what is your required field type? what's filled in it, and is there ANY rules on it.
from the ribbon> home tab> click on rules. Now click on the required field and check if there's any rules on it (field rules will appear in the Rules panel after you click on the field).
also..
You can always go to Data tab from the ribbon> select
Rules Inspector to view all rules written in your form.
good luck
let me know how it goes.
Aabed