There are some things you can check first.
If it's a nominal posting do you have access to that nominal.
Can postings be made of that posting type on other matters.
Is a valid client linked to your matter?
If it looks like your posting should be ok to go through then it could be possible that as part of workflow there are letters being generated off the back of your posting.
Sometimes these letters include complicated math and as part of that transaction it runs through this math and will lock the system for any other postings until this is complete.
To check if the system lock is due to this.....
Click Posting Maintenance on the main menu.
Click on the Letters tab.
Select the Case Type from the drop down of the case they are having issues posting on.
Scroll down through the transaction types to the one causing the system lock. Is there anything in the Letter column?
Make a note of the Memo or Letter being produced by the transaction type found in the grey box next to Document.
Now click on Workflow Maintenance from the main menu.
Select either Letter/Fax/Email or Memos tab depending on what was being produced from the Posting Maintenance Letters tab.
Find your Letter or Memo in the list, the document name is from the Document box in posting maintenance letters tab.
Click on your letter or memo and look down in the right bottom corner.
In the Update Details box is the Before? or After? Box ticked and is there anything in the two grey boxes next to this?
If so it is likely that this After or Before math is what is causing your system lock on postings.
If you are unsure or if you do not have access to Posting Maintenance or Workflow Maintenance then you can raise a new case online and reference the title of this article.