user33979: I am experiencing a recurring problem with my BitCoin Core wallet. The main issue here is that I get an error message every so often as the program is updating the transaction blocks. 
Please see the jpeg in the link above, this is the exact error message I get when the client is updating.
Details:

I am using BitCoin Core V 12.0
I have tried reindexing using : c:\Program Files\Bitcoin\bitcoin-qt.exe -reindex
I have tried to reinstall the client, then restart my computer, then open and let it update.
I haven't yet tried a RAM test to see if my RAM could be the source of corrupted data
I'm running Windows 7 OS 64-bit, 8Gb DDR3 RAM

I feel its something that can be fixed with a patch, but I could be wrong. If anyone has a solution that I can try myself, that would be most welcome. 

user6256: It is possible that you are running out of RAM or HDD space.  Check this github report from a user with a similar issue.  If this is not the case then I would run a memtest and see if you don't have an issue with your RAM.

33979: <p>I am experiencing a recurring problem with my BitCoin Core wallet. The main issue here is that I get an error message every so often as the program is updating the transaction blocks. <a href="https://i.stack.imgur.com/PQFlE.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/PQFlE.jpg" alt="Assertion failed error"></a></p>

<p>Please see the jpeg in the link above, this is the exact error message I get when the client is updating.</p>

<p>Details:</p>

<ol>
<li><p>I am using BitCoin Core V 12.0</p></li>
<li><p>I have tried reindexing using : c:\Program Files\Bitcoin\bitcoin-qt.exe -reindex</p></li>
<li><p>I have tried to reinstall the client, then restart my computer, then open and let it update.</p></li>
<li><p>I haven't yet tried a RAM test to see if my RAM could be the source of corrupted data</p></li>
<li><p>I'm running Windows 7 OS 64-bit, 8Gb DDR3 RAM</p></li>
</ol>

<p>I feel its something that can be fixed with a patch, but I could be wrong. If anyone has a solution that I can try myself, that would be most welcome. </p>
 6256: <p>It is possible that you are running out of RAM or HDD space.  Check <a href="https://github.com/bitcoin/bitcoin/issues/6196" rel="nofollow">this</a> github report from a user with a similar issue.  If this is not the case then I would run a memtest and see if you don't have an issue with your RAM.</p>
