strange behavior with Server Internal Error 500

[dmitrievskiy.alexander85]

Hello! Thank you for your service! It's very useful.

I have 2 questions:
1)
When I have uploaded web-site-sources via ftp I stuck with problem Internal Server Error 500.
And the strangest thing is the solution of the problem: If I delete the php file of the page with the error from the server (let it be for example "map.php") and reupload it - no error happens with this particular file! What does change reuploading of files(the files are the same)?

I can reupload all my web site. But I would like to understand what does cause such problems.

2)
My web site needs PEAR libraries. I have installed the local pears with pear-go into "~/tools/" folder. And further, pear-scripts needs to be added into include_path.
I tried to add them in .htaccess file with

php_value include_path ".:/usr/local/lib/php:/home/myusername/tools/PEAR"

but this (and variations of this) creates INTERNAL SERVER ERROR 500 For web pages. After deleting everything correct but pathes. So my next question is: "Where is mistake and how can I set includes in .htaccess file?"
So now I should add into every my script string

set_include_path('/home/myusername/tools/PEAR:/home/myusername/public_html');

But it a little bit annoying and path depend (if something change I should fix all this paths in every file(()

Thank you for replies Sorry for my English

---------- Post added at 05:36 AM ---------- Previous post was at 05:26 AM ----------

Seems I found an answer to my first question. The problem was due to 0777 permissions.

But second question is still open. Hope on your help