I reinstalled my InvoicePlane server to a much newer machine. 
It is running on windows 10 under wamp 3.
I can create a quote, but I cannot directly create an invoice.
I can see all the old invoices, quotes, clients, etc. but I can’t create a new invoice.
I get this error.
Failed to load resource: the server responded with a status of 500 (Internal Server Error)
mysql is not in strict mode.
Did you followed the instructions from the FAQ about general errors?
Yes.
This is the error from Chrome’s dev console:
https://paste.invoiceplane.com/view/5ea154d6
Yes.
There were no error logs for mysql, php, or in /application/logs.
Debug mode is enabled.
I think I know what your problem is. I had the same issue when I tried installing this for the first time today. Have exact setup, and got the exact same error. I had to go to the root of the InvoicePlane Install and change the htaccess to .htaccess and also do the portion of the install pertaining to installing in a subdirectory. Every project within wamp is a subdirectory so that is probably why it is happening. Here is the link to what to do to the .htaccess to get it to work.
https://wiki.invoiceplane.com/en/1.0/getting-started/installation#subdir
Also in case you didn’t know windows won’t let you rename htaccess to .htaccess from within file explorer. You can, however, open it in notepad, and do save as. when there make sure to change the file type to All Files (.) and it will let you save it as .htaccess.
And just to add, in the installation instructions it is easy to overlook the part that the htacces modification is required for it to work. I also tried running this on both a centos and ubuntu server where I used apache virtual hosts as well and put it in the root of that virtual host and it is doing the exact same thing. So it seems that the only time you do not have to do that is if it is truly installed in the server’s webroot.
Hope this Helps