Th program crashes the moment I click on the "Open". button in the window where I select the file to attach.
I don't know if it contains some information you can use, but this is the core dump info:
Process: iCash [1841]
Path: /Applications/iCash/iCash.app/Contents/MacOS/iCash
Identifier: com.maxprog.icash
Version: 7.6.3 (7.6.3.3.0)
Code Type: X86-64 (Native)
Parent Process: ??? [1]
Responsible: iCash [1841]
User ID: 501
Date/Time: 2018-04-04 15:39:32.212 +0200
OS Version: Mac OS X 10.13.4 (17E199)
Report Version: 12
Anonymous UUID: F889AD04-B8F2-E86B-7892-197BC974E58B
Time Awake Since Boot: 16000 seconds
System Integrity Protection: enabled
Crashed Thread: 0 Dispatch queue: com.apple.main-thread
Exception Type: EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: KERN_INVALID_ADDRESS at 0x0000000000000008
Exception Note: EXC_CORPSE_NOTIFY
Termination Signal: Segmentation fault: 11
Termination Reason: Namespace SIGNAL, Code 0xb
Terminating Process: exc handler [0]
VM Regions Near 0x8:
-->
__TEXT 000000010d8c7000-000000010f9f1000 [ 33.2M] r-x/rwx SM=COW /Applications/iCash/iCash.app/Contents/MacOS/iCash
Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0 libvshared_fat_release_x64.dylib 0x00000001134fea82 fbl::String::c_str() const + 4
1 v4rb_cocoa_64.dylib 0x00000001129a12ed Str_Unicode::c_str() const + 13
2 v4rb_cocoa_64.dylib 0x00000001129af8bb Field_SetString(REALobjectStruct*, REALstringStruct*) + 200
3 com.maxprog.icash 0x000000010da92a56 VField.SetString%%o<VField>s + 54
4 com.maxprog.icash 0x000000010dcf2c73 boTransaction.SetAttachmentMacInfo%%o<boTransaction>i8ss + 403
5 com.maxprog.icash 0x000000010eefdfca Dlg_Main.Dlg_Main.Transaction_Attachment_Add%%o<Dlg_Main.Dlg_Main>o<Listbox> + 7450
6 com.maxprog.icash 0x000000010eb32759 Dlg_Main.Dlg_Main.Interface_CM_Transactions%%o<Dlg_Main.Dlg_Main> + 95977
7 com.maxprog.icash 0x000000010e5b74ce Dlg_Main.Dlg_Main.LB_Transactions_MouseDown%b%o<Dlg_Main.Dlg_Main>o<cListBox>i8i8 + 238
8 com.maxprog.icash 0x000000010f0aeb54 Delegate.IM_Invoke%b%o<cListBox>i8i8 + 68
9 com.maxprog.icash 0x000000010e265552 AddHandler.Stub.37%b%i8i8 + 98
10 com.xojo.XojoFramework 0x000000011009368c RuntimeListbox::HandleClick(MouseEvent const&) + 86
11 com.xojo.XojoFramework 0x000000010ff80271 0x10fe99000 + 946801
12 com.xojo.XojoFramework 0x000000010ff7b413 0x10fe99000 + 926739
13 com.apple.AppKit 0x00007fff2f58b43d -[NSWindow(NSEventRouting) _reallySendEvent:isDelayedEvent:] + 5040
14 com.apple.AppKit 0x00007fff2f589c70 -[NSWindow(NSEventRouting) sendEvent:] + 497
15 com.xojo.XojoFramework 0x000000010ff7c57c 0x10fe99000 + 931196
16 com.apple.AppKit 0x00007fff2f3eb236 -[NSApplication(NSEvent) sendEvent:] + 2462
17 com.xojo.XojoFramework 0x000000010ff6bf9d 0x10fe99000 + 864157
18 com.maxprog.icash 0x000000010d91a005 Application._CallFunctionWithExceptionHandling%%o<Application>p + 181
19 com.xojo.XojoFramework 0x00000001100ec4df CallFunctionWithExceptionHandling(void (*)()) + 262
20 com.xojo.XojoFramework 0x000000010ff6bf18 0x10fe99000 + 864024
21 com.apple.AppKit 0x00007fff2ec4b8b5 -[NSApplication run] + 812
22 com.xojo.XojoFramework 0x00000001100ea80b RuntimeRun + 40
23 com.maxprog.icash 0x000000010d9d9923 REALbasic._RuntimeRun + 19
24 com.maxprog.icash 0x000000010f8d1638 _Main + 536
25 com.maxprog.icash 0x000000010f8cc893 main + 19
26 libdyld.dylib 0x00007fff59a7d015 start + 1