Hello I am getting the error:

* Transaction 'T000000000000000198' post date '2015-02-03' is older than opening date '2015-07-06' of account 'Cat1:Subcat'.
Account opening date updated. Finished: 1 problem corrected. 0 problems still present.

This error occurs on every transaction. I can not find the post date only a date of the transaction
Can I lose data on this error and where can I find the post date?

You don't say what version you are using - that would help!

In the latest version (4.7.2) the consistency checker has changed and it seems to be rather more "aggressive".

Where a transaction has been posted before the opening date of the account (typically due to import of transactions), the consistency checker should update the account opening date. This is what the output of the consistency checker is telling you in the example you provided.

No data loss has occurred and the "problem" has been fixed. You don't have to do anything.

There are instances where the consistency checker does not change the account opening date and you need to do it manually - if you want to stop the output from the consistency checker...

Nice to know that there is no lost of information.
So do I understand it correctly. The openings date is the date which I entered in the account information panel under the tab general?
If so I don't know why the error occurs. The openings date of my account is 31-12-2014 and the imports are form 2-1-2015

I am using version 4.12.5 under Win7 64bit

The opening date mentioned in the message belonged to a category. Categories are also accounts which had opening dates (by default the date that you created your file), this is now fixed but a new version with this fix isn't yet released, anyway there is no data loss involved.

using 4.6.6

so when entering opening data in a category the date is actually greyed out and can't be changed - I see the default is the date of creating the category but how can one enter an opening balance at, say, the beginning of the year?

OK - I solved this in the new version I downloaded 4.7